LIGHT
INTRODUCTION:
You can
see an object only if light from it enters your eyes. When light energy enters
the eye, it affects the nerves at the back of the eyeball which transmit signals
to the brain. Some objects such as the sun, electric lamps and candles make
their own light. We call these luminous sources.
Most things we see do not
make their own light but reflect it from a luminous source. These are the
non-luminous sources e.g you and the page you are looking
at.
Luminous sources
radiate light when their atoms become excited as a result of receiving energy.
In a light bulb for example, the energy comes from electricity. Sun beams
streaming through trees and light from the cinema projector on its way to the
screen both suggest that light travels in straight lines. The beams are visible
because dust particles in the air reflect light into our
eyes.
The direction of
the path in which light is travelling is called a ray and is represented in
diagrams as a straight line with an arrow on it.
A
beam is a stream of light and is shown by a number of rays. It maybe parallel,
diverging(spreading out) or converging(getting narrower).
Parallel
diverging
converging
SOME PROPERTIES OF
LIGHT
1. Light can travel through a
vacuum (i.e it does not have to be carried by a medium) e.g light from the sun
travels most of the distance to the earth through a
vacuum.
2. light moves at a very high
speed(quickly) V= 3 x
108m/s
3. a shadow is produced when
light passes an obstacle and this suggests that light travels in straight
lines.
EXPERIMENT TO DEMONSTRATE
THAT LIGHT TRAVELS IN STRAIGHT LINES (RECTILINEAR
PROPAGATION)
Apparatus: 3 card board
screens having small holes in their centers.
- Candle or lamp.
Diagram
A
B
Method: Arrange the apparatus as shown so that the holes are in a straight line by threading a string through the holes and pulling it tight. Place the light source at A and view from B.
Observation:
i)
light at A can be received by an eye at B.
ii) if however one of the screens is moved so that the holes are nolonger in a straight line, the light is cut off.
SHADOWS (area of
shade)
When an obstacle is placed in the path of light coming from a point source, the shadow formed on a screen is uniformly dark and has sharp edges. As no light reaches the region of shadow(umbra), it is concluded that light travels in straight lines.
Point source
shadow(umbra)
obstacle
screen
If an extended light source is used, the shadow is edged with a border of partial shadow(penumbra).The area of partial shadow receives light from some points on the source.
Shadow(umbra)
Partial
shadow
Obstacle
screen
(penumbra)
Extended source
ECLIPSES
When the moon passes between
the earth and the sun, the moon’s shadow falls on the earth. We call this an
eclipse(solar eclipse) of the sun by the moon.
Sun
moon
earth
B
A
C
Region A- The
Umbra
People standing in this
region see a total eclipse.
Regions B and C- the
Penumbras
People watching from these
regions receive some light energy and see a partial
eclipse.
(The tip of the umbra fails
to reach the earth’s surface)the sun’s appearance is a ring of
light
On
some occasions the moon is a little further from the earth and a partial eclipse
is formed.
Sun
Moon
D Earth
This is an annular eclipse.
The central part of the sun is hidden but not its outer
parts
N.B: There was an eclipse of
the sun on June 30th 1973 in the afternoon. All over Uganda the sun
was at least 80% obscured(hidden).In certain places in Uganda and Kenya, the
eclipse was total. A total eclipse seen from one place may last for up to 7
minutes. During this time although it’s day, the sky is dark, stars are visible,
the temperature falls and birds stop singing.
When the earth comes in
between the earth and the moon, we get what we call the eclipse of the
moon(lunar eclipse).
sun
E
1
2
3
Why
don’t we see an eclipse very oftenly?
The
plane of the moon’s orbit is not the same as that of the earth around the sun.
We therefore have to wait until the sun, moon and earth are all in a straight
line.
THE PINHOLE CAMERA
The
pinhole camera operates on the principle that light travels in straight lines to
produce a clear image.
A pinhole camera may be made
by removing the back of a small card board box and replacing it with a piece of
semi-transparent paper(the screen).A pinhole is made in he side of the box
opposite the screen. When the hole is is held towards a bright lamp, such as a
carbon filament lamp(candle light)in a darkened room, an inverted Image of the
lamp filament can be seen on the screen.
Screen
B
A
A
Inverted, diminished image
Bright lamp
B
Each point on the object is
responsible for a point of light on the screen and a complete inverted image is
seen.
If
the pinhole camera is moved closer to the lamp, the image becomes
bigger.
The
small hole ensures that little light enters the camera. A larger hole would
improve this but would lead to a blurred(distorted) image unless a lens was
used(because it acts as a ray gatherer, bringing the many images to one
point).
Near object with a pinhole
camera
Several holes, rays can fall
at different points on the screen.
B
A
B
A
When the hole is enlarged, a
wide cone of rays can fall on the screen, so the image is
blurred.
Magnification(calculation
method incomplete)
REFLECTION AT A PLANE SURFACE
When light is incident on a
surface, it is either transmitted, absorbed or reflected.
-Absorbed: its energy is converted into
other forms usually heat and it is no longer light.
-Transmitted: it passes throughout the
material of the object as when light passes through water in a bowl. It may change its
direction at the surface.
-Reflected: it is sent away from the
surface again and is now travelling in a different
direction.
There are two different
kinds of reflection.
1. Regular(specular) reflection:
This is the reflection of
light in a particular direction. It occurs with mirrors and also with smooth
objects such as polished furniture and glossy magazines.
2.
Diffuse or Irregular
reflection:
This is the scattering of
light in all directions by the rough surface of an object.
a) rough surface
plane
mirror
PLANE MIRRORS
Some metals are good
reflectors of light and they reflect more than 90% of the light incident on
them. A plane mirror is usually a flat piece of glass coated with a thin layer
of silver or alminium at the back and protected by a coat of paint. Incident
rays travelling towards the mirror are reflected by the metal by regular
reflection to form images. The rays strike and leave the mirror at the point of
incidence. The normal is the line at right angle to the surface at the point of
incidence(angles of incidence and reflection are measured from the normal)
Laws of
Reflection:
1.
The incident, normal and reflected rays to the surface at the point of
incidence, all lie in the same plane(can be drawn on flat sheet surface of
paper)
2.
The angle of incidence equals the angle of reflection.
–
verify laws
–
parallax
–
rotation of mirrors
TO STUDY THE IMAGE MADE IN A
PLANE MIRROR:
A straight line MM’ is drawn across the center of a sheet of drawing paper to represent a reflecting surface and a large letter E to serve as an object. A strip of plane mirror is then stood vertically with its silvered surface over MM’ and the image located.
I1
I5
I2
I6
I4
I3
M
M ¢
O2
O6
O3
O4
O1
O5
Method: stick object pins
O1,O2,----- on the object letter
and each time the images I1,I2,--- are located by the
method of nor parallax using a search pin.
The
image in a plane mirror is;
1) the same size as the
object
2) the same distance behind the
mirror as the object is in front.
3)
laterally inverted.
4)virtual(cannot be formed
on a screen)
(as
compared to the image in a pinhole camera, that is said to be
real.)
HOW
THE EYE SEES AN IMAGE IN A PLANE MIRROR
O
I
IMAGES FORMED IN TWO MIRRORS
INCLINED AT 90O
I1
I2
I3
O
Each mirror forms its own
image by a single reflection but a third image is formed by a double
reflection.
If the angle between mirrors
is µ, then the number of images
h is got by
h = 3600 1
µ
\ Two parallel mirrors,
µ = 00 , then h =
3600 1
0
infinitely
many images.
Applications
1. The Periscope:
450
O
450
Consists of two mirrors
fixed facing each other and inclined at an angle of 45? To the stem of the
periscope. The observer uses the periscope to see over the top of
obstacles.
It
is used in submarines(but in a more complex form)
2. The Kaleidoscope
mirror mirror
Mirror
Three mirrors inclined at
angle 600 to each other and fixed inside a ligh-proof
tube.
Look through from the top
A glass plate at the bottom
of the tube admits light. Small pieces of coloured glass are placed on the glass
plate. These act as objects and on looking through the tube, fine images are
seen as well as the objects. This forms a symetrical pattern with six(6)
identical sectors. When the pieces of glass are rearranged by shaking the tube,
fresh patterns are formed and the number obtainable is unlimited(used by artists
to get patterns of colours. A kaleidoscope can also be made using two
mirrors.
O
600
I1
I5
I4
I2
I3
Qn.
The angle between the incident ray and a plane mirror is
250;calculate
i)
the angle of
incidence
ii)
the angle of
reflection
iii)
the angle turned through by the ray of
light
Assignment:
a) The laws of
reflection
b)
the description of the image formed by a
plane mirror
c) the meaning of the words real and
virtual when used to describe images.
REFLECTION AT CURVED SURFACES
The laws of reflection apply to
reflectors of any kind and all shapes. A curved mirror is a small part of the
surface of the sphere.
Axis
P
C
C F
P
F
Terms:
-
The center of curvature is the
center of the sphere of which the mirror forms part.
-The radius of curvature ¡ is the radius of the
sphere.
-
The pole: of the mirror is the centre of
the reflecting surface.
-
The principal axis is the imaginary line
joining the pole and the centre of curvature produced in each
direction.
- The principal focus: is the point on the
principal axis through which rays parallel to and close to the axis pass after
reflection(concave mirror)or from which the rays appear to come(convex
mirror)
-
The Focal length f is the distance between
the principal focus and the pole of the mirror.
Note: Rays that are not parallel
to the principal axis strike the mirror at an
angle and leave the mirror
at the same angle.
¡
Reflection of wide parallel
beams by spherical and parabolic mirrors.
C
F
P
F
P
A caustic
curve
Only rays parallel to and
near the principal axis pass through the principal focus. When a very wide beam
of rays is incident on a concave mirror, the rays not near the principal axis
are reflected to points nearer to the mirror than the principal focus. Instead
of a bright sharp image, the rays form a bright curved image called a caustic
curve. A bright caustic curve can often be seen on the surface of tea in a cup.
This is formed when light from a distant lamp is reflected from the inside of
the cup which acts as a curved mirror of large aperture.
A parabolic curved mirror
forms a sharp focus. The mirrors in head lamps and search lights are therefore
parabolic rather than spherical. They form parallel beams from a lamp at their
focus(in connection with the reversibility of light)
The special rays for use in
constructing curved mirror ray diagrams
1.
C
F
P
P
F
C
A ray parallel to the
principal axis reflected through F
2.
P
P
F
C
C
F
A
ray arriving through F is reflected parallel to the principal
axis.
C
F
P
P
F
C
A
ray arriving through C strikes the mirror at right angles and returns along the
same path through C.
Images formed by a concave mirror
a) 
object O between F and
P
Image
I is
i) virtual
P
ii) erect
C
F
O
iii) magnified
iv) behind the mirror
b) object O at
F
Image
I is at infinity
C
F
P
b) 
object O between F and
C
Image I is
C
F
P
I) real
ii) inverted
iii) magnified
iv)
beyond C
d) Object O at C
Image I is
i)
real
ii) inverted
iii) same size as object
C
F
iv) also at C
C
F
e) object O beyond
C
C
F
C
F
Image I is
i) real
ii)
inverted
iii) diminished
iv)between C and F
f)
object O at infinity
Image I is
i) real
ii) inverted
iii) diminished
C
F
iv) at F
In c, d and e, object and
image positions are examples of conjugate foci.
N.B: A real image is formed by
the actual intersection of rays whereas a virtual image is one formed by the
apparent intersection of rays when their directions have been produced
backwards.
The
image formed by a convex mirror
O
P
F
C
Image
is;
i)
virtual
ii)
ii)
erect
iii)
iii)
diminished
iv)
iv) between F and P, behind
the mirror
Note: The mirrors considered
above are small in size or aperture compared with their radii of
curvature
Mirrors of large aperture
Conjugate foci are any pair
of points such that an object placed at one of them gives rise to a real image
at the other. Therefore an object and its real image can be interchanged. This
follows the principle of reversibility of light.(the path of light ray can be
reversed in either direction)
C
F
A ROUGH METHOD OF MEASURING
THE FOCAL LENGTH OF A CONCAVE
MIRROR
Procedure:
-
Hold a concave mirror at on
end of a room, facing a distant window.
-
hold a white screen infront
of and facing the mirror so that it receives rays reflected from it but allows
rays to reach the mirror from the window.
- move the screen to different
distances from the mirror until a sharp image of the window is
formed.
- measure the distance from
the screen to the mirror with a meter ruler.
Measuring the radius of
Curvature of a concave mirror.
Apparatus:- A light box with an illuminated object
(An
upright sharp arrow drawn on a translucent paper covering a circular hole
infront of a light box forms a suitable illuminated
object)
-
With the mirror facing the
illuminated object, adjust the distance between them until a sharp image is
formed on the screen alongside the object. This image will be sharpest when it
is exactly the same size as the object.
- Measure the distance object and
the back of the mirror.
- Repeat the measurement with the
same attempts at finding the position of the sharpest image and calculate an
average value for the radius of curvature of the mirror.
- Divide of your result by two(2)
for the focal length of the mirror.
R = 2f
lamp
light box
- Accurate ray
construction
- mirror
formula-??
- (Real is position
convention)
Qn.1. Using a mirror with
radius of curvature 20cm,determine the full details of the image when an object
1.5cm high is placed at a distance of 4cm from the mirror.
2. An object 2cm high is situated on and
perpendicular to the axis of a concave mirror of radius of curvature 30cm and is
10cm from the mirror. Find the position and size of the
image.
Uses of curved
mirrors
1. Car head lights and sport
lights
2. 2. Shaving mirrors; the
shaving mirror is a concave mirror and it forms a magnified virtual, upright
image.
3. The driving mirrors; a
driving mirror is convex since it gives a wide field of view compared to a plane
mirror of the same size. It also gives an erect image but of a smaller
size.
plane
narrow field of view
wide field of view
REVISION
QUESTIONS
1.
(a) State the laws of
refraction of light.
(b) A
swimming bath contains water to a depth of 2.6m. Taking the refractive
index
of water to be 1.3,
i)
find the apparent depth of
the water.
ii)
If there is a plane mirror
on the floor of the bath, how far from the object will the reflected image of
the person floating on the surface of the water be?
2 a) Define the following
terms as used in the study of waves.
i) Refraction ii) Deffraction iii) Interference
b) Give two differences and
similarities between sound waves and light waves.
c)
A girl stands between two
high cliffs which are at distance of 500m apart. She stands at a distance 210m
from one cliff and claps her hands. What time elapses after she hears the first
echo and before she hears the second echo?
3a) i) State the laws of reflection of
light.
ii) Describe one experiment to verify one of the
laws.
iii)Explain reflection of a
parallel beam of light falling on a rough surface.
b) A pin 5.0cm high is placed on
and perpendicular to the principal axis of a concave(converging) mirror of
radius of curvature 4.0cm. The pin is placed 15cm away from the pole of the
mirror. Construct a ray diagram to determine the position and magnification of
the image of the pin formed.
A
film
Qn.4
lens
B
10cm
The
diagram above shows a simple camera. The lens has a focal length of
10cm.
a) Name parts A
and B.
b) At what
distance should the object be placed from the lens for a clear image to be
formed on the film?
c) Find the
height of the image formed when an object 2m high is placed 5m in front of the
camera.
5. a) Draw a labeled diagram to show
the eclipse of the sun.
b) From the
formation of eclipses, what conclusion can be drawn about
light?
6. a) Explain why a girl walking on a
tarmac road sees a pool of water she never reaches.
b) (i) Describe the nature of images
formed by a pin-hole camera.
(ii) What is the effect of making
the pin-hole bigger?
c) A pin-hole camera has its screen 9cm
from its hole, it forms an image of a tree 100m away and 25.2cm
high.
(i)
Find the magnification of the camera.
(ii) Calculate the height of the
image formed.
7.a) (i) State the laws of refraction of
light.
(ii)A ray of light from air makes an angle of 30deg. With a boundary
separating air and glass. Find the refractive index of glass with respect to
air, given that the angle of refraction in glass 35deg
16?.
b)
An erect object 6cm high is placed at a point 25cm from a convex lens. The real
image of the object formed by the lens is 3cm high. Construct a ray diagram and
use it to find;
i)
the focal length of the
lens.
ii) the power of the
lens.
c)
When is a convex lens used;
(i) as a magnifying
glass?
(ii) in a
projector?
8.a) Show how a ray of light
passes through a 600 prism.
b) (i) If the angle of incidence at one
face of the prism is 450 and the angle of refraction at the same face
is 26.20, what is the refractive index of the prism
material?
(ii) At what angle to the normal does
the ray emerge from the second face of the prism?
9.a) A concave mirror has a
focal length of 4cm and a real object 2cm tall is placed 9cm away from it. By
means of an accurate full size diagram, find where the image would be and
measure its length.
B
200
A
C
Fig.6
(b)
Fig.6 shows rays in a semicircular glass block.
i) Explain why the ray entering the glass
at A is not bent.
ii) Explain why ray AB is
reflected at B and not refracted.
iii) Ray CB does not stop at B. Draw a
small sketch and draw its approximate path after it leaves
B.
c)
An object is placed 4cm in front of a convex lens. A real image is produced 16cm
from the lens. What is the magnification produced by the
lens?
L
10.
White
screen
B
A
M
A
ray of white light AB is directed onto a glass prism as shown in the
diagram;
a) Complete the ray diagram to
show how the light is refracted through the prism.
b) Why does the glass prism refract
white light as you have shown?
11.
A swimming bath contains water to a depth of 2.6m. Taking the refractive index
of water to be 1.3,
a) what is the apparent
depth of the water?
b) If there is a mirror at
the floor of the bath, how far from the object will the reflected image of a
person on the surface of the water be?
c) Draw a clearly labeled
diagram of the eye to show how short sightedness is
corrected.
d) Give three similarities
between the eye and the pin-hole camera.
12.a) State the laws of
refraction of light.
a)
What is meant by refractive
index of a medium?
b)
An erect object of 5cm high
is placed at a point 2.5cm from a convex lens. The real image of the object
formed by the lens is 2.5cm high. Construct a ray díagram and use it to find the
focal length of the lens.
13.
Draw scale diagrams to show the images of the following objects as viewed
through the lenses.
a) i) An object A of height 5cm
perpendicular to the principal axis of a converging lens, at a distance of 20cm
from the lens. The focal length of the lens is 12cm.
ii)An object B of length 4cm
perpendicular to the principal axis of a diverging lens, at a distance of 10cm
from the lens. The focal length of
the lens is 15cm.
b) i) What is the distance of the
image of A?
ii) What is the distance of the image
of B?
14.
Define;
a)
Focal length of a
mirror.
b)
Pole of a
mirror.
15.
A concave mirror focuses on an object which stands vertically upwards on its
principal axis 120cm away. The image formed at 200cm away from the mirror. By
means of an accurate scale drawing, determine the focal length, nature and
position of the image.
16.a) Draw a diagram of a
pin-hole camera to show how the image of an object is
formed.
b)What is the effect on the
image formed by the pin-hole camera when;
i) the hole is
increased in size?
ii) the object distance
from the camera is increased?
17.a) With the aid of
diagrams, explain the differences between the reflection of light which
occurs;
i) from a
flat sheet of white cloth.
ii) from a flat
sheet of shiny alminium foil.
b)State four properties of
an image formed by a plane mirror.
c)
A man sits in an optician’s
chair looking into a plane mirror 1.8m away from him. He views the image of a
chart 0.7m behind his head and facing the mirror. How far from his eye does the
chart appear to be?
d)
An object of height 2cm is
placed 8cm from a concave mirror of focal length 4cm. Using a scale diagram,
find the nature, position, height and magnification of the image
formed.
e)
State any two applications
of concave
mirrors.
18.
a) Define critical angle, dispersion and total internal
reflection.
b) Show by a ray
diagram how a right-angled prism may be used to turn a ray of light
through,
i) 900 ii)
1800
iii) State any one
application of total internal reflection.
c) An insect hovers above still water of
a pond. Draw a ray diagram to show approximately where it appears to be to a
fish in the water vertically below it.
d) Find by construction the focal length
of the concave lens which produces an image 1cm high of an object 2cm high
placed 12cm from the lens.
19.
Copy and complete the ray diagrams below.
p
f
f
mirror
20.
a) Draw a labeled diagram to show a spectrum of white light is formed by a rain
drop to produce a rainbow.
b) Draw a
labeled overlapping circle to show the primary and secondary colours of
light.
c) i) Draw a ray diagram showing how a
lens may be used as a magnifying glass.
ii) Name the type of
lens used.
iii) Describe the
image formed by the lens in this way.
An object is placed 8cm from
a convex lens of focal length 3cm. By graphical construction, find the position
of the image formed.
21.a) Define
i) A mirage
ii)
Total internal reflection
b) Complete the
diagram below.(which represents 3 rays of light from a point object O in water
and incident on a water-interface) to show how the rays behave at the
interface.
air
water
O
22.a) Define:
i)
the principle focus of a converging lens.
ii)
a virtual image.
b) With the aid of a
labelled diagram, describe a simple experiment to determine the focal length of
a converging lens.
23. An object of height 4cm is
placed perpendicularly on the principal axis at a distance
of
45cm from a converging lens of focal length of 15cm.
a)
By graphical construction
determine;
i) the position of the image.
ii) the
magnification.
b) Give one use of
converging lenses.
24.a) Define refractive
index of a medium.
b) A ray of light from air enters
a liquid medium at an angle of incidence of 45deg. If the angle of refraction is
28deg, calculate the refractive index of the liquid.
25.a) State the laws of
reflection of light.
b) M1
3cm
O
4cm
M2
An
object O is placed 3cm and 4cm from mirrors M1 and M2
respectively which are inclined at 900 to each other. What will be
the distance between the image of O in M1 and in
M2?
26.
a) Describe an experiment to verify one of the laws of reflection of
light.
b) A pin 5cm
high is placed on and perpendicular to the principal axis of a concave mirror of
radius of curvature 4.0cm. The pin is placed 15cm away from the pole of the
mirror. Construct a ray diagram the position and magnification of the image of
the pin formed.
27.a) Explain with the aid
of diagrams, the terms ‘total internal reflection’ and critical
angle.
b) Light of the same wave length
is incident at angle i, on a glass prism. The light is refracted and follows the
path shown in the figure below.
Find
the angle of incidence i.
480
i
420
c) Explain the appearance of a
blue flag with red stripes when viewed in day-light through a sheet of yellow
glass.
28.
a) Define:
i) the principle focus of a converging lens.
ii) a virtual
image.
b) With the aid
of a labelled diagram, describe a simple experiment to determine the focal
length of a converging lens.
c) An object of height 4cm
is placed perpendicularly on the principal axis at a distance of 45cm from a
converging lens of a focal length of 15cm.
By graphical construction
determine:-
i) the position of the
image
ii) the
magnification.
d) Give one use of
converging lenses
29. a) i) Describe a simple experiment to show
that light travels in a straight line.
ii)An object 3cm high
is placed at right angle to the principle axis of a concave mirror of focal
length 7.5cm. If the object is 30cm from the pole of the mirror, construct a ray
diagram to obtain the position and size of the image formed
iii)State two
applications of a concave mirror.
b) i) State the laws of
refraction of light.
ii)Light of the same
wave length is incident from air on glass of refractive index 1.5. If the angle
of incidence is 60o, find the angle of refraction.
30. a) i) State the laws of
reflection of light.
ii)
Define focal length of a converging lens.
iii)
Describe a simple experiment to determine the radius of curvature of a concave
mirror.
b) Light is
incident on a glass prism at an angle as shown in the figure
below.
180
i
420
Find:- i) the refractive
index of the prism
ii)
the angle of incidence.
c) A pin
5cm high is placed perpendicular on the principal axis at a distance of 27cm
from a convex lens of focal length 15cm.
i)
By graphical method, find the image distance.
ii)
Calculate the magnification.
d) Show by
use of prisms how the colours of the spectrum can be recombined to form white
light.
31. a) Draw a diagram to
show why a pool of water appears shallow when viewed from
above.
b)Light is
incident in air at an angle of 32? To an air-glass boundary. If the refractive
index of glass is 1.5, find the angle of refraction.
32. a) Define dispersion of
white light.
b)
400
water
340
glass
A
ray of light is incident on a water glass boundary at an angle of 40?. If
refractive index of glass is 1.5, calculate the refractive index of
water.
33.
a) State the laws of reflection of light.
b) With the aid
of a diagram, show how a concave mirror can be used as a shaving
mirror.
c) An object of height 1cm
is placed 7cm from a concave mirror of focal length 5cm. Using a scale diagram,
find the position, nature, height of the image formed and the
magnification.
d) Describe an experiment to determine
the focal length of a concave mirror.
34. a) Describe an
experiment to show that light travels in a straight line.
b) An
object of height 4cm is placed 5cm away from a pinhole camera. The screen is 7cm
from the pinhole;
i)
Draw to scale a ray diagram to show the formation of the image by the pinhole
camera.
ii)
What is the nature of the image formed
iii)
Find the magnification.
iv)
Explain what happens to the image if the pinhole is made
larger.
c) Draw a diagram to show the formation
of a scalar eclipse.
35. a) i) Describe a simple experiment to show
that light travels in a straight line.
ii)
An object 3cm high is placed at a right angle to the principal axis of a concave
mirror of focal length 7.5cm. If the object is 30cm from the pole of the mirror,
use graphical method to obtain the position and size of the image
formed.
iii)
State two applications of concave mirrors.
b) i) What
is meant by the terms
Principal focus and pole of a concave mirror?
ii)
Draw a diagram to show how concave mirror produces a magnified virtual image of
a suitably placed object, and show where an eye must be positioned in order to
see the image.
36. a) What is refraction of
light?
b) A ray of
light is incident at one face of a glass prism as in the diagram
below.
600
i
400
If
refractive index of glass is 1.5, calculate the value of angle
i.
37.
a) Draw a ray diagram to show the formation of an image of an object which is
perpendicular to the principal axis and infront of a convex
mirror.
b) State one
application of a convex mirror.
38.
a) Define the following terms:-
i) Real image
ii)Virtual image
iii)Principal focus of
a mirror.
iv) Centre of
curvature
v) Pole of a
mirror.
b)
A concave mirror of focal length 40cm, focuses an object which is 20cm away and
5cm in height. By means of an accurate scale diagram,
determine:-
i)
The nature of the
image.
ii) Image
distance
iii) Magnification
c) State one application of
a concave mirror.
40.
a) State the laws of reflection of light.
b) With the aid
of a diagram, show how the eye sees the image of an object through a
mirror.
41.
a) Name any four evidences that show that light is propagated
linearly.
b) i) State laws
of reflection.
ii) Name the different types reflections. Explain briefly the type of
reflection you would expect when light falls on a piece of cotton
cloth.
c) The distance
between an object and its enlarged real image produced by a concave mirror is
20cm when the object is placed 100cm from the pole of the
mirror.
42.
a) Explain why a pinhole camera produces a sharp image, and why the image
becomes blurred if the pinhole is enlarged.
b) An object 10cm from
a pinhole camera of length 10cm produces an image of width 5cm. What is the
width of the object?
43.
An object is placed perpendicular to the principal axis between the principal
focus and the optical centre of a convex lens.
Sketch a ray diagram to show
the formation of an image of the object.
44.
a) What is meant by refractive index of a medium?
i
water
35.50
glass
b)
A ray of light is incident on the water glass boundary and refracted at an angle
of 35.5?. Calculate the angle of incidence if the refractive indices of water
and glass are 1.33 and 1.5 respectively.
45.
a) Define the following terms with reference to curved
mirrors:-
i) Centre of
curvature
ii)
Pole
iii) Principal
focus
b) Draw a ray diagram to
show how a parabolic mirror can be used to produce a parallel beam of
light.
c) The focal length of a
concave mirror is 10cm and an object is placed at a distance of 30cm from the
mirror. Using a scale drawing, find:-
i) the position of the image
ii) its magnification
iii) nature of the image.
