4th form

Hosted by www.Geocities.ws

4th form 4th form Physics 2005/2006

Welcome to 4th form Physics. This page will contain invaluable information which will help you through the year. Make sure that you bookmark it!

4P 14/12/05

We performed an experiment to test how the acceleration of an object varied when we changed the unbalanced force acting on it.

We found that the acceleration was proportional to the force.

The gradient of the graph depended on how hard it was to accelerate the trolley we were using - this depended on the mass. (It is harder to accelerate a more massive object.) The gradient of the graph should have given us the mass of the trolley plus additional masses, however, as we ignored friction it wasn't quite correct.

4C 14/12/05

What on Earth did we do? Probably an experiment in which we varied the mass of a trolley, keeping the accelerating force the same. The acceleration dropped as the mass got larger in accordance with Newton's second law (F=ma).

HW Plot the graph of acceleration against mass.

4P 12/12/05

Cover work was collected in from last time. We looked at a question on car stopping distances which used the idea that the area under a speed vs time graph gives you the distance travelled and the gradient is the acceleration.

We then looked at some questions based on Newton's 2nd law - F = ma.

Heavy objects are harder to accelerate - it takes a larger force to give them the same acceleration as a less massive object. Indeed, the definition of 1 Newton of force is: "The force required to give an object of 1kg an acceleration of 1m/s/s.

HW None - printers down... RP owes me P70-71 though and LC, RP, TB (and other resitters) need to do an electronics test revise for next time please.

4C 09/12/05

We performed an experiment to test how the acceleration of an object varied when we changed the unbalanced force acting on it.

We found that the acceleration was proportional to the force.

HW P74 Qs 2,5,6 (and revise for a little control in electronics retest if you are AB, RC or SF)

4P 07/12/05

RM absent - you did work from the AQA book Ps 72-78?

4C 07/12/05

RM absent - you made notes on the forces and motion section of AQA.

4P 05/12/05

Control in electronics resits for next lesson.

We looked at motion graphs and what they represented.

We learned that the gradient of a distance against time graph tells you the speed of an object.

The gradient of a speed against time graph tells you the acceleration of an object.

The area underneath a speed against time graph tells you the distance travelled by an object.

HW Little graph fill in sheet.

4C 02/12/05

Very much as 4P below. Control in electronics resits next lesson!

4P 30/11/05

The promised resit for control in electronics will be soon.

Forces and motion was introduced. Measuring motion was the first order of business and has been largely covered by all of you in the 3rd form.

Average speed = Distance / Time

Light gates and ticker tape timers (ttts) as methods of measuring speed were recapped.

A ttt produces one dot every 1/50th of a second.

The distance between the dots varies if the speed is changing.

We looked at calculating acceleration.

Acceleration is the rate of change of speed (as long as no change of direction is involved)

Acceleration (m/s²) = Change in speed / time

In symbols : a = (v-u)/t

v = final speed (m/s)

u = initial speed (m/s)

t = time to go between the 2 speeds

We used a ttt to measure the acceleration due to gravity of an object. The expected result would be about 10 m/s/s but yours were a bit smaller due to the friction caused by the ticker tape.

HW AQA P 70/71 All Qs.

4C 30/11/05

We went through the control in electronics test.

4P 28/11/05

We went through the control in electronics test. For the most part this was done very well indeed..... A few people missed the test, Louis' test went missing and a couple of lowish marks means that those guys will do a resit soonish.

Yellow sheet on Qs mentioned below goes out today.

4C 25/11/05

Identical to 4P below.

I need to see the cover work from all who were present last Friday please. "Using Transistors" sheet qs 1-4 is missing from some people also. These are also on P294/295 of Physics Matters.

4P 23/11/05

We sat the long control in electronics test.

We also looked at some completely ridiculous questions which are also drawn from genuine past papers. Be aware that you will come across some total waffle questions that are no more Physics than Mr Mackrell is a ballerina.

You were reminded that non production of "Using Transistors" sheet qs 1-4 and Qs 8 + 10 P61-63 of the AQA book will draw a yellow sheet by the end of the week.

4C 23/11/05

We did some practise GCSE questions for a test which will be on Friday on all control in electronics. All that you needed to know was listed on the board - resistor colour codes, logic gate symbols and truth tables, potential divider calculations, transistors as switches turned on by a high enough voltage at the input, thermistors and LDRs as input sensors, capacitors as time delays (they take some time to charge up to full voltage, the time taken can be increased by putting them inseries with a larger resistor or increasing the size of the capacitor), relays must be used to make a transistor circuit operate a high power device, a reverse biased diode is needed to stop the relay breaking the trasistor.

HW Revise, perhaps by finishing off the last few of those questions. Please tell Sam Feldman, Ben Hedley etc. about the test.

4P 21/11/05

We prepared ourselves for a control in electronics test which will take place on Wednesday. Qs 8 and 10 from your AQA P61-63 must be given in on Wednesday, stay of execution of a yellow slip due to CCF.

HW Revise for a test - use the past paper questions I have given you to practise.

4C 18/11/05

RM @ CCF. Cover work.

4P 16/11/05

We described in exacting detail how a capacitor can be used in place of one of the resistors to create a time delay in a potential divider circuit.

We then attempted plenty of problem on transistors and sensing circuit from "Physics through applications".

HW Q8 P61/62 and Q10 P62/63 from the AQA book.

4C 16/11/05

We introduced the capacitor. They are, simply put, a gap in the circuit in which 2 parallel metal plates are held close together but not touching.

The battery still tries to push electrons around the circuit, but can't as there is no complete circuit.

However, some electrons are "pulled" away from the capacitor plate attached to the positive end of the battery leaving it with an overall positive charge. Similarly, electrons are pushed onto the other plate by the negative end of the battery leaving it with a negative charge.

For a small amount of time, as charge is building up on either plate, a current moves around the rest of the circuit.

Eventually, the battery is unable to push any more charge onto the plates and the current stops flowing. The capacitor is now charged up to the same voltage as the battery. The voltage across a charging capacitor therefore varies over time. This is very useful as it can allow you to add a time delay to a potential divider circuit.

We plotted a graph of the voltage across a capacitor as it charged up. There are 2 ways of slowing down the capacitor charging. One is to get a larger capacitor, the other is to charge it in series with a larger resistor.

HW Selection of recap questions on electronic control (handout).

4P 14/11/05

We did a little recap of control in electronics so far.

Then we moved onto capacitors. They are, simply put, a gap in the circuit in which 2 parallel metal plates are held close together but not touching.

The battery still tries to push electrons around the circuit, but can't as there is no complete circuit.

For a small amount of time, as charge is building up on either plate, a current moves around the rest of the circuit.

HW Plot the graph of voltage against time for the charging capacitor using the results we took in the lesson. I still need "using transistors" sheet in from many of you, a new yellow sheet is due any time.

4C 11/11/05

RM absent. You had a go at electronic control questions from the AQA book.

4P 09/11/05

You were given a brief overview of how transistors actually work. The hand out attempts to explain this in terms of the chemicals involved etc. They are essentially a sandwich of 2 different types of silicon. Only when a voltage is applied to the middle section can the whole thing conduct electricity.

Combinations of transistors can be used to make "logic gates". The rest of the lesson was extremely similar to 4C's lesson below.

We actually tested some physical logic gates, although the ones in a real live application would be somewhat smaller.

HW Have another go at the Using Transistors questions 1-4 and get them in to me before next lesson (yellow sheet will go out on Friday)

4C 09/11/05

More on transistors, and we then looked at how transistors can be combined to make logic gates. 2 transistors in series both need to be switched on in order for them to conduct. They make up an AND gate. Only one of 2 transistors in parallel needs to be switched on for there to be conducting path.

Warning: when logic gates are shown as part of an electronic circuit, a simplified version is shown. i.e. you can't see all the wires.

You need to know the symbols and the "truth" tables for 3 types of logic gate. Truth tables just tell you what state the output of the gate is for any combination of inputs.

A NOT gate placed directly after an AND gate can be shortened to:

HW Finish copying the tables down for the 3 gates and answer Qs 1 and 4 from page 52 of the AQA book. MAny failed to get the last set of HW in, have another go and hand it in before next lesson, or a yellow sheet awaits you.

4P 04/11/05

A transistor is an electronic switch. It turns on when the input voltage reaches a certain "switching" level, and it then conducts electricity, turning on any devices in series with it.

You are not required to know the details of how a transistor works, however, I gave you a handout attempting to explain this to you anyway. Intel fit many millions of transistors onto their chips, and this is what they have to say about them... I will furnish you with a handout that attempts to explain how the transistor works at an atomic level next time. This is purely for your interest however, and is not required knowledge for the GCSE.

The above are the circuit symbols for transistors (don't worry too much about the different types)

A potential divider circuit can be used to provide the input voltage to the transistor. This is particularly useful if the potential divider contains a component like a thermistor. As the external temperature increases, the resistance of the thermistor falls, and the voltage across the thermistor gets smaller. A transistor can be used to switch on a warning light when the temperature gets too high/low.

The above circuit turns on the lamp when light levels hitting the LDR get higher.

Adam R will join me in 509 on Wednesday break time.

HW Qs 1-4 from the Using transistors sheet need to be done.

4C 04/11/05

A transistor is an electronic switch. It turns on when the input voltage reaches a certain "switching" level, and it then conducts electricity, turning on any devices in series with it.

Current can only pass all the way through the silicon sandwhich when a voltage is applied to the middle portion.

The above are the circuit symbols for transistors (don't worry too much about the different types)

The above circuit turns on the lamp when light levels hitting the LDR get higher.

HW Qs 1-4 from the Using transistors sheet need to be done.

4P 02/11/05

We went through the test first of all. A reasonable effort on the whole except for Adam R who will join me at 1.30pm tomorrow in 509. (JL too)

We made a type of potential divider circuit with a thermistor put in as one of the resistors. The thermistor loses resistance as the temperature rises, so this changes the voltage across both components in the circuit. A voltmeter can be placed in the circuit to make a simple thermometer. We made one and tested its function at different temperatures.

HW Design a similar circuit to the one that we built today which will act as a light meter. Then, try to build a circuit that will turn on a light when it is dark (this is much harder).

4C 02/11/05

We sat a test full of GCSE questions on electricity. On with control in electronics next time.

HW None, some people still owe me some past work though. PM P237 Qs 1-5 for instance.

4P 31/10/05

We sat a test full of GCSE questions on electricity. On with control in electronics next time.

HW None, some people still owe me some past work though.

4C 21/10/05

We then just began to look at potential dividers. They are simply series circuits which split up the battery voltage between components.

The "output voltage" above depends upon the resistance of the 2 resistors. You could work out the voltage across each resistor using Ohm's law.

Firstly calculate the current in the entire circuit:

I = V / R_T

Where R_T = R₁ + R₂

(because the 2 resistors are in series you add them together to find the total resistance of the circuit.)

The current is the same through both resistors because they are in series. You can calculate the voltage across them using Ohm's law again. (V = IR)

V_R1 = I R₁

(and the same for R₂)

However, there is a shortcut formula which sidesteps calculating the current. You simply know that each resistor takes the same proportion of the total voltage as its proportion of the total resistance of the circuit.

Algebraically, this looks a bit like this:

HW Finish your graph and the explanation of how the circuit worked. Revise for a test full of GCSE questions by doing AQA P59-60 Qs 1 to 4

4P 19/10/05

We did some practice questions on power in circuits. These can be found in Physics Matters P236-237 and should be finished for HW. Using both V = IR and P = IV in questions is often necessary.

For cost of electricity questions, you must use the formula:

Energy used = Power * Time

but the power must be measured in kiloWatts and the time in hours.

We learned to work out the resistance of a resistor using the colour codes on it.

You will always be given the table below, so there is no need to learn the colours.

We learned an alternative formula to calculate the resistance of 2 resistors in parallel.

R_T=R₁R₂/(R₁+R₂)

We then just began to look at potential dividers. They are simply series circuits which split up the battery voltage between components.

The "output voltage" above depends upon the resistance of the 2 resistors. You could work out the voltage across each resistor using Ohm's law.

Firstly calculate the current in the entire circuit:

I = V / R_T

Where R_T = R₁ + R₂

(because the 2 resistors are in series you add them together to find the total resistance of the circuit.)

The current is the same through both resistors because they are in series. You can calculate the voltage across them using Ohm's law again. (V = IR)

V_R1 = I R₁

(and the same for R₂)

Algebraically, this looks a bit like this:

HW Variously..... Finish questions from PM P236/237, do question 3 from AQA P59 and revise all electronics for a test full of genuine GCSE questions next half term.

4C 19/10/05

We learned to work out the resistance of a resistor using the colour codes on it.

You will always be given the table below, so there is no need to learn the colours.

HW Physics Matters P236/237 Qs 1-5

4P 17/10/05

We too saw the electrical safety video. The important points you need to know are:

1. Earth wires are needed to prevent the outside of an electrical appliance from accidentally becoming live.

2. The main danger from poor wiring is fire, not electrocution.

3. The correct fuse must be fitted to each appliance, but also the correct thickness of power cable must be used.

4. Don't do any of the internal wiring in your house yourself, call a qualified electrician.

HW Do Qs 1-4 on the colourful sheet about electrical safety.

Adam R, Ott H-F and Adam W owe me an extra question from PTA as they were trying to finish their homework in the lesson.

People who had to redo the test but haven't given it to me yet must make that their priority, before grades are done tomorrow!

4C 14/10/05

We went through the test.

Then we saw a film on electricity in the home. Using too thin wire to plug in high power devices was shown to be dangerous. High currents through thin wires can cause fires.

Fuses and Earth wires as safety devices were shown.

We then discussed the cost of electricity. The amount of electrical energy used by your home is not measured in Joules as is normal, but in kiloWatt hours. (kWh).

1 kWh = energy used by a 1000W device left on for 1 hour.

To calculate how many kWh a device is using, convert its power rating from Watts into kiloWatts. Then work out how much time it has been left on for in hours.

Energy used = Power * time

Each kWh costs about 7-10p so you can then work out the expense.

HW AQA P27 Qs 2,3,5 and P30 Qs 1 and 2.

Those who got under 50% in the test will return to me a set of correct answers by next lesson.

4P 12/10/05

Test results were awful. We went through it, those who got under 50% will return a pristine set of answers by next time.

We also wired some plugs. A fuse is a fire prevention device - it stops large currents flowing accidently causing heating which might start a fire.

We saw where the fuses actually go. They are put into the plug of a device attached to the "live" pin.

The other 2 pins of a plug are the neutral and the Earth. The live and the neutral connection are the 2 that join the circuit in normal operation (just like connecting to both ends of a battery really.)The Earth pin is a safety measure which stops the outer case of an electrical device becoming charged by the live wire accidently. If ever the live wire were accidently to touch the outer case, a large current would flow down the Earth wire and the fuse would melt. This is described well on the BBC website here

We tried to wire some plugs ourselves, some of you are much better than me at it. Others may need to practise a bit before doing it for real....

At home, electricity is supplied as alternating current. This happens because the current is being pushed by an alternating voltage. Electrons actually go backwards and forwards within the wires 50 times a second.

HW Finish off Qs 1235 from P27 of the AQA book.

4C 12/10/05

We sat the electricity test, marks next time with luck.....

HW - None except for those who have catch up to do.

4P 10/10/05

We sat the electricity test. Some still have missing HWs, another yellow sheet will be issued next lesson.

4C 07/10/05

We did some practice calculations on P = IV, with particular reference to fuses. A fuse is a safety device which melts when too much current is flowing through it. The "size" of fuse chosen to go in the plug of a particular appliance tells depends on how much current the device uses in normal operation. This is calulated using the formula:

Current = Power/Voltage or I = P/V

You choose a fuse value which is above the amount of current which the device would normally use, but not too large so that unsafe levels of current can flow.

A fuse is a fire prevention device - it stops large currents flowing accidently causing heating which might start a fire.

We then looked at where the fuses actually go. They are put into the plug of a device attached to the "live" pin.

We tried to wire some plugs ourselves, some of you are much better than me at it. Others may need to practise a bit before doing it for real....

More on this and electrical safety next week.

Note to self: We did not cover the cost opf electricity.

HW Revise for a test which will be full of simple calculations using Ohm's law (V=IR) and power in circuits (P=IV). Also on the menu will be a question about electrostatics and the amount of electrical charge used in a circuit (Q=It)

4P 05/10/05

Apparently no takers for the cube of resistors. Chocolate still up for grabs.....

We looked at some bulbs which had different power ratings. Power is a measure of how fast something converts energy from one form into another.

Power = Energy/time

Bulbs with higher power ratings are brighter. Remember, power is calulated by:

P = IV

We used the above formula along with E = VQ and Q = It to do a series of calculations about energy in circuits.

You pay for electricity in your home based on the amount of energy you use (transfer from electrical energy into other forms which are useful to you). The Joule is rather too small a unit to use if you want to add up the energy that you have used for an entire quarter. A different unit, the kilowatt-hour (kWh) is used instead.

1kWh = the energy used by a 1kW device that has been left on for 1 hour.

1kWh is 1 "unit" on your electricity bill and typically costs about 7p.

In order to calculate how many units a particular device is using you must do the following things:

1 - Find the power of the device and convert it into kW. (e.g. 100W = 0.1kW)

2 - Convert the time that it has been left on for into hours. (this is the only time that times should not be measured in seconds in Physics)

3 - Units used = Power (kW) * Time (hours)

You can find the expense by simple multiplying the number of units by the cost per unit.

HW Revise for a test which will be on Ohm's law (V=IR) and P=IV as well as electrostatics.

Adam Rostowski, Luke Jones and Josh Mallalieu will all meet me in 509 at the beginning of tomorrow lunch.

4C 05/10/05

We tried a couple of practice resistor addition questions.

Then we looked at the power of electrical components. All convert electrical energy into other forms which vary depending upon the component.

The rate at which they convert energy is known as their power.

Power = Energy converted / time It is measured in Watts or Joules per sec

Current is the rate of flow of charge ( 1 Amp = 1 Coulomb per second)

Current = Charge/time or I = Q/t

Q represents charge just as I represents current.

Voltage is a measure of energy per unit charge (1 Volt = 1 joule per Coulomb)

Voltage = Energy/charge or V = E/Q

E is energy

So multiply the current by the voltage and you get a measure of how much energy is converted per second.

Power = Current * Voltage or P = IV

HW Do Qs 1-7 from page 22 and 23 of AQA book

Catch up with everything, everybody! I'm doing yellow sheets today, make sure that your name isn't on them!

4P 03/10/05

We looked at energy and power in circuits. Voltage is a measure of the energy given to each Coulomb of electrical charge as it passes through the battery (or the energy used up as it passes through each component).

Voltage = Energy/Charge or V = E/Q

Current is a measure of the number of Coulombs of charge which flow around the circuit each second.

Current = Charge/Time or I = Q/t

Combining these 2 quantities, tells you how much energy is being transferred each second (which is the same as power).

Energy use per second = Voltage * current = Power or P = IV

Remember that power is measured in Watts, which are the same as Joules per second.

HW Bring in a home electricity bill for next time. Several people are way behind at the moment. Yellow sheets will be issued tomorrow regardless of absences. The website is there for a reason - get caught up!

4C 30/9/05

Actually identical in every detail to 4C's lesson below!

With the exception that we looked at a demo relevant ot the next topic. Electricity is useful because it can tranport energy from one place to another. We saw an electrical generator used to power some light bulbs. It was much harder to turn the generator when all of the light bulbs were connected. More energy was required from the person doing the turning, as more elctrical energy was then needed to provide more heat and light energy for the light bulbs. We learn how to calculate the amount of energy used by electrical components next time.

HW Q3+4 P233 of Physics Matters

4P 28/09/05

We learned how to add up resistances in series and in parallel. We also formalised the 2 important rules in electrical circuits.

The first rule states that the currents entering a junction must equal the currents leaving a junction. In this case, I₁ + I₃ = I₂

This above rule also implies the important fact that the current is the same at all points in a series circuit. (Where there are no junctions.)

The second rule states that the battery voltage of a circuit must be used up in total by all of the components in series.

The sum of potential differences across components = battery voltage

In parallel circuits, the voltage is the same across each parallel path.

Resistors in Series

Simply add them up!

R₁ + R₂ = R_Total

Resistors in parallel

1/R₁ + 1/R₂ = 1/R_total

This is a little harder, as you have to be able to do some maths. Here is an example:

A 3 Ohm resistor is put in parallel with a 12 Ohm resistor, what is the total resitance?

1/R₁ + 1/R₂ = 1/R_total

So 1/3 + 1/12 = 1/R_total

1/3 = 4/12

4/12 + 1/12 = 1/R_total

= 5/12

Cross multiplying gives: R_total = 12/5 = 2.4 Ohms

Your answer will always be somewhat smaller than either of the 2 resistances in parallel.

We spent some time practising these calculations. We'll move onto energy and power in electrical curcuits next time.

HW Q3+4 P233 of Physics Matters

4C 28/09/05

We noted down some important facts about non-Ohmic conductors. A thermistor loses resistance as the temperature rises. It is not made of metal, but of a semi-conductor. The semi conductor shakes loose more "free" electrons as it heats up, and so starts to conduct electricity to a much better degree, thereby reducing its resistance.

We also looked at an LDR (light dependent resistor) which works in a nearly identical fashion, but uses light energy to give it more free charge carriers. An LDR therefore loses resistance as the light level goes up.

Both of these components are very important in sensing circuits, which we will cover in much more detail later on.

HW Finish off sheet 1.4 for next time.

4P 26/09/05

A further experiment was carried out to test the voltage against current relationship for a component.

We tested a thermistor with the same circuit used to test the bulb and resistors previously. It was found that the thermistor had a varying resistance depending on the temperature it was at.

3 sets of voltage and current readings were taken at 3 different temperatures. The slope of the lines was significantly different for each temperature, getting less steep, the hotter the temperature became.

Unlike ordinary conductors, a thermistor loses resistance when it heats up. It does this because it is made of a non metallic material called a semi-conductor. The semi-conductor does not have very many free charge carriers available to conduct electricity at low temperatures. However, when it is heated up, the extra vibrations cause more electrons to lose their stable position and become free to conduct.

Resistance vs. temperature for a thermistor.

HW Finish the 3 graphs if not already done so, and calculate the gradient of each one. Complete sheet 1.3 and 1.4 (on reverse side)

Several people failed to get Qs 4-6 P19 (AQA) handed in. Tomorrow or yellow sheets! Cardboard folders for next time.

4C 23/09/05

A further experiment was carried out to test the voltage against current relationship for a component.

We tested a thermistor with the same circuit used to test the bulb and resistors previously. It was found that the thermistor had a varying resistance depending on the temperature it was at.

Resistance vs. temperature for a thermistor.

HW Finish the 3 graphs if not already done so, and calculate the gradient of each one. Complete sheet E5 on varying resistance for next time.

NB I did not take in the HW from everyone (AQA P19 Qs 4,5,6) so I must remember to get this in aswell next time!

4P 21/09/05

The experiment to test how voltage applied across a component effects the current flowing through it was done on a 220 ohm resistor and a 6V light bulb

The resistor showed a proportional relationship between the voltage and the current. It is said to obey Ohm's law.

The gradient of line gives the resistance of the component.

Voltage = Current times Resistance, or V = IR, R = V/I

It was found that for the light bulb the voltage and current were not proportional to each other. The line on the V/I graph was a curve. This means that the bulb does not obey Ohm's law. (Resistance = Voltage / Current).

This graph has opposite axes to the one you plotted. Don't worry about this, the important point is that the hotter the bulb gets, the greater the voltage increase required to push more current through the filament.

Hotter objects have an increased resistance

This file shows my data with a graph plotted.

This is due to more particle vibrations, which means that electrons are involved in more collisions as they try and flow through the material.

HW AQA P19 Qs 4,5,6 - read the section on resistance first.

4C 21/09/05

The experiment to test how voltage applied across a component effects the current flowing through it was done on a 6V light bulb (in mA this time).

It was found that the voltage and current were not proportional to each other in this case. The line on the V/I graph was a curve. This means that the bulb does not obey Ohm's law. (Resistance = Voltage / Current).

Hotter objects have an increased resistance

This file shows my data with a graph plotted.

This is due to more particle vibrations, which means that electrons are involved in more collisions as they try and flow through the material.

HW AQA P19 Qs 4,5,6 - read the section on resistance first.

4P 19/09/05

We finished off electrostatics by looking at the Van der Graff generator. It puts such a large charge on a metal dome by friction that it can cause a spark to fly through the air. Air does not usually conduct electricity, but it becomes ionised with the large electric field present meaning that the charge can escape to Earth if a suitable Earthed object is near enough the dome.

All objects which touch it and are not Earthed become charged too, causing the famous vertical hair effect.

If a sharp point is added to the dome while it is charged, it causes a lot of ionisation at its tip. A stream of charged ions is "blown" away from the point (we saw 2 sharp points causing a piece of metal to rotate due to this.) Using this method, lightning conductors actually work to avoid lightning strikes in their area altogether. If lightning does strike, it will pass through the conductor rather than the building, however.

Lightning is dangerous due to the collosal amount of charge being moved. Other, much smaller sparks can be dangerous if there are volatile chemicals about.

4C 16/09/05

We started the electricity topic. We defined what electric current and voltage were.

Current: the rate of flow of electric charge (Amps)

1 Amp refers to 1 Coulomb (the unit of charge) of charge flowing past a point in 1 second.

Voltage: the size of electrical "push" trying to cause a current to flow (Volts)

1 Volt refers to 1 Joule of potential energy being given to each Coulomb of charge.

An electrical conductor has charge carriers (usually electrons) which are free to move, thus they allow an electrical current to flow when a voltage is applied to them.

You built and tested a circuit that can be used to see how the current and voltage across an electrical component vary in comparison to each other.

You found that voltage and current were proportional for both the components we tested. These components obey Ohms law: Current is proportional to current, the constant of proportionality is called resistance.

V = IR (Your graph may have had different axes, allowing the gradient to equal the resistance of the component.)

HW Calculate the gradient of your straight line of best fit for each unknown resistor. This should equal the resistance of the components you tested.

We will need to do the light bulb experiment again, in mA!

4P 14/09/05

Photocopying and electrostatic spray painting were looked at, aswell as electrolysis.

Electrolysis occurs when dissolved ions are attracted towards either a positive or negative electrode immersed into a solution. The solution is effectively conducting electrical current, although it is unusual as it is ions which are moving as opposed to electrons.

A little site explaining elecrolysis in more detail (it's Chemistry really). We will finish off electrostatics on Monday.

Meanwhile, we started the electricity topic very briefly. We defined what electric current and voltage were.

Current: the rate of flow of electric charge (Amps)

1 Amp refers to 1 Coulomb (the unit of charge) of charge flowing past a point in 1 second.

Voltage: the size of electrical "push" trying to cause a current to flow (Volts)

1 Volt refers to 1 Joule of potential energy being given to each Coulomb of charge.

You built and tested a circuit that can be used to see how the current and voltage across an electrical component vary in comparison to each other.

We will use the same circuit again to test other components later.

HW Do the questions found at the end of the "Electrostatics revision sheet" for next time

..........................................................

GCSE maths Q:

Q: how many times can you subtract 7 from 83, and what is left afterwards? A: I can subtract it as many times as I want, and it leaves 76 every time.

4C 14/09/05

We took some notes on uses of electrostatics.

Earthing cables and lightening conductors are both safety devices to avoid the dangerous effects of electrostatics. Spray painting devices and photocopiers both make use of electrostatics in order to work.

HW Questions from the revision sheet on electrostatics. Qs 2,3 and 5 were taken in. Books must be with me by tomorrow if they aren't by today.

Some more uses of electrostatics...

.............................................................

What's the difference between mechanical engineers and civil engineers? Mechanical engineers build weapons. Civil engineers build targets.

4P 12/09/05

RM absent. You took some notes on uses of electrostatics.

4C 09/09/05

We rubbed polyethene rods with dusters, and found that 2 such rods slightly repelled each other. (we used a low friction watch glass device to establish this). Electrons had been "scraped" from the duster onto the polyethene, leaving both negative and therefore repelling each other. Other materials were found to charge positive when rubbed by the duster (they attracted the polyethene).

The gold leaf electroscope shows when it has a charge on it because the charge on the gold leaf and on the metal next to it are alike. The gold leaf is repelled by the metal next to it and therefore is held away at an angle. Materials can be charged by rubbing with a cloth. Different materials will charge differently when rubbed by the same cloth. It depends which materials "scrapes" electrons off which. The material which loses electrons gains an overall positive charge (it has more protons than electrons) and the material which has gained electrons has a negative charge.

A charged object will also attract something that is neutral. Think about how you can make a balloon stick to the wall. If you charge a balloon by rubbing it on your hair, it picks up extra electrons and has a negative charge. Holding it near a neutral object will make the charges in that object move. If it is a conductor, many electrons move easily to the other side, as far from the balloon as possible. If it is an insulator, the electrons in the atoms and molecules can only move very slightly to one side, away from the balloon. In either case, there are more positive charges closer to the negative balloon. Opposites attract. The balloon sticks. (At least until the electrons on the balloon slowly leak off.) It works the same way for neutral and positively charged objects.

We looked at sparks caused by electrostatic charging. If an object becomes highly charged enough, then it will try to discharge in any way it can. Sometimes, the electrical force has become so large that the air itself becomes ionised, allowing it to conduct. This is when a spark is seen.

Interesting site on electrostatic weather......

HW Physcics Matters P221 Qs 2,3,5

........................................................

There are 10 kinds of people in the world..... Those who understand Binary, and those who don't.

4P 07/09/05

Welcome to GCSE Physics. Text books were issued and numbers recorded. Ringbinders were issued, these are what you keep your notes in.

The GCSE course has a 20% coursework element which you don't need to worry about until much later.

We will be kicking off by looking at electrical charge. Protons are heavy and positive and live in the nuclei of atoms. Electrons are light and mobile and negative and surround the nucleus at some distance, held in by the electrostatic attractive force.

Chemical reactions can cause atoms to lose or gain electrons and become charged. They are then known as positive or negative ions. However, we'll leave them to the chemists. Another way that materials can become charged is by friction.

HW Physcics Matters P221 Qs 2,3,5

......................................................

Two atoms bump into each other. One says 'I think I lost an electron!' The other asks, 'Are you sure?', to which the first replies, 'I'm positive'

4C 07/09/05

Welcome to GCSE Physics. Text books were issued and numbers recorded. Ringbinders were issued, these are what you keep your notes in.

The GCSE course has a 20% coursework element which you don't need to worry about until much later.

Cracking electrostatics page

.......................................................

A neutron walks into a bar; he asks the bartender, 'How much for a beer?' The bartender looks at him, and says 'For you, no charge.'

Hosted by www.Geocities.ws