Physics ICSE Class 7 Important Questions Chapter 4 Light
Additional Questions
A. Tick (√) the following questions.
Question 1.
Light help us in making objects –
(a) invisible
(b) visible
(c) disappear
(d) none of these
Answer:
(b) visible
Question 2.
Light travels in a –
(a) circle
(b) zig-zag path
(c) straight line
(d) random path
Answer:
(c) straight line
Question 3.
When light falls on an object it –
(a) cast shadow
(b) glare
(c) sparkles
(d) shine
Answer:
(a) cast shadow
Question 4.
Planets cast their shadows in –
(a) mare
(b) earth
(c) sun
(d) space
Answer:
(d) space
Question 5.
Sometimes, on a full moon day, the moon passes through the shadow of –
(a) Earth
(b) Mars
(c) Mercury
(d) Venus
Answer:
(a) Earth
Question 6.
The number of shadows that fall on the moon due to Earth during a lunar eclipse is –
(a) one
(b) two
(c) none
(d) three
Answer:
(b) two
Question 7.
The umbra is a –
(a) half dark shadow
(b) half light shadow
(c) full dark shadow
(d) half dark shadow
Answer:
(c) full dark shadow
Question 8.
The penumbra is a –
(a) full outer shadow
(b) full inner shadow
(c) partial inner shadow
(d) none of these
Answer:
(d) none of these
Question 9.
The principle of working of a pinhole camera is –
(a) rectilinear theory of light
(b) non rectilinear theory of light
(c) wave theory of light
(d) corpuscular theory of light
Answer:
(a) rectilinear theory of light
Question 10.
The number of lens a pinhole camera has –
(a) one
(b) nil
(c) two
(d) three
Answer:
(b) nil
Question 11.
For, lunar eclipse, there should be alignment of –
(a) only Sun and Earth
(b) only Sun and Moon
(c) Sun, Earth and Moon
(d) only Earth and Moon
Answer:
(c) Sun, Earth and Moon
Question 12.
Total lunar eclipse is sometimes called as –
(a) blue moon
(b) white moon
(c) black moon
(d) blood moon
Answer:
(d) blood moon
B. Answer the following questions.
Question 1.
Explain the phenomenon of reflection.
Answer:
The coming back of light in ‘a medium after striking the surface of some other medium is called reflection of light. Explanation : Suppose you hit a wall with a ball. The ball will be returned to your side.
If you shout in an empty hall. Your voice comes back after hitting the walls of the hall.
Question 2.
Define the terms plane, normal to the plane, point of incidence, angle of incidence and angle of reflection.
Answer:
Plane : A flat or fully levelled surface is called plane.
Normal : It is the perpendicular drawn at the point of incidence. In figure ON is the normal.
Point of incidence : The point where the incident ray strikes the reflecting surface is called point of incidence.
Angle of incidence : Angle between the normal and the incident ray made at the point of incidence is called angle of incidence.
Angle of reflection : Angle between the normal and the reflected ray made at the point of incidence is called angle of reflection.
Question 3.
State the law of reflection.
Answer:
Law I. The angle of incidence is always equal to angle of reflection, that is, angle PON = angle QON, that is, l = r
Law II. The incident rays, the reflected ray and the normal, all are in the same plane.
Question 4.
Describe reflection of light from a plane mirror.
Answer:
If a ray of light is originated from a point P and strike the plane mirror at Q such that line PQ makes an angle of 90° with the mirror then this ray of light will be returned back by the plane mirror along same path in the direction QP.
Question 5.
Use law of reflection to show formation of image by a plane mirror.
Answer:
To demonstrate the reflection of light by a plane mirror and draw ray diagram to show reflection by mirror.
Material required :
Drawing Board, a white sheet of paper strip of plane mirror, modelling clay (say plasticine), paper pins, pencil, rubber, scale, protractor (D).
Procedure :
1. Fix white sheet of paper on the drawing board.
2. Fix plane mirror on the lengthwise edge along a straight line M1M2 using modelling clay. Mark a point O in the
middle of line M1M2 Draw ON normal on line M1M2 at point O.
3. Draw a line OP such that angle PON is acute, that is, less than 90°. Fix two pins at points P1 and P2 on the line OP.
4. See the images of pins P1 and P2 in the mirror. Fix pins P3 and P4 on the white sheet of paper such that they are in line with the images P1‘ and P2‘ seen in the plane mirror.
5. Remove the plane mirror and mark the positions of pins by drawing small circles around the pins. Join position P3 and P4 to get line OQ.
6. Now OQ is the reflected ray, OP is the incident ray and ON is the normal.
7. Measure angles PON and QON. Here angle PON is the angle of incidence (i) and angle QON is the angle of reflection (r).
Observations and Result :
(i) We find that angle of incidence i is equal to angle of reflection r.
- We also see that incident ray, reflected ray and normal all lie in the same plane of paper.
- This activity verifies the first and the second law of reflection.
Question 6.
Describe the characteristics of image formed by a plane mirror.
Answer:
Characteristics of the image formed by a plane mirror :
(a) The image is formed behind the mirror and it is at a distance equal to distance of the object in front of the mirror.
(b) Size of the image is equal to the size of the object.
(c) Image is obtained when reflected rays from the mirror are extended backward (such an image is called I or I).
(d) Image appears laterally inverted in a plane mirror.
Question 7.
State the value of speed of light.
Answer:
Speed of light in Transparent Materials
Question 8.
State primary colours.
Answer:
The group of Red (R) Green (G) and Blue (B) colours from which all other colours can be had by mixing are called primary colours.
Question 9.
Describe formation of secondary colours by addition of primary colours.
Answer:
Important secondary’ colours are :
(a) Magenta (or purple)
(b) Cyan
(c) Yellow
If primary colours blue and red are mixed we get magenta (or purple) colour. That is, Blue + Red = Magenta.
If primary colours green and blue are mixed we get cyan colour
Green + Blue = Cyan
If primary colours red and green are mixed we get yellow colour
Red + Green = Yellow
Question 10.
Explain the observed colour of an object based on reflection and absorption of light of different colours from the object.
Answer:
Ordinary Sunlight consists of light of all colours. When this light strikes an opaque object it absorbs some colours which will not reach our eyes. Other colours of the light are reflected back or sent to our eyes. This reflected or transmitted colour of light decides the colour of the object.
For example if an object absorbs light of all colours except green then the object will look green.
C. Tick (✓) the best choice :
Question 1.
Light is a form of –
(a) work
(b) power
(c) energy
(d) none of these
Answer:
(c) energy
Question 2.
Light causes sensation of –
(a) vision
(b) touch
(c) smell
(d) taste
Answer:
(a) vision
Question 3.
Branch of science which deals with light is called
(a) electronics
(b) optics
(c) kinetics
(d) dynamics
Answer:
(b) optics
Question 4.
A shining surface absorbs
(a) electronics
(b) optics
(c) small amount of light
(d) very large amount of light
Answer:
(c) small amount of light
Question 5.
A Laser beam is basically
(a) sound
(b) light
(c) current
(d) magnetic
Answer:
(b) light
D. Fill in the blanks :
Question 1.
The ray of light which strikes a reflecting surface is called ……………
Answer:
The ray of light which strikes a reflecting surface is called incident ray.
Question 2.
The ray of light returned by the reflecting surface to the same medium is called
Answer:
The ray of light returned by the reflecting surface to the same medium is called reflected ray.
Question 3.
The perpendicular drawn at the point of incidence is called …………..
Answer:
The perpendicular drawn at the point of incidence is called normal.
Question 4.
Mirror of cooker is used to reflect sun light on …………. the food.
Answer:
Mirror of solar cooker is used to reflect sun light on the food.
Question 5.
Plane mirror can be used by a driver to see ………… view.
Answer:
Plane mirror can be used by a driver to see back view.
E. Tick the true and false.
Question 1.
Speed of light in air is 2,25000 ms-1.
Answer:
False.
Question 2.
Objects produce same sensations in the eye when they reflect or emit light.
Answer:
False.
Question 3.
Newton found more than 10 colours in white light.
Answer:
False.
Question 4.
Red, green and yellow are primary colours.
Answer:
False.
Question 5.
Mix red, green and yellow to get white.
Answer:
False.
F. Match the following :
| A. Plane mirror | a. 2,25,000 ms2 |
| B. Submarine | b. periscope |
| C.Speed of light in water | c. 1,24,000 ms2 |
| D. Speed of light in diamond | d. flat surfaced mirror |
Answer:
| A. Plane mirror | d. flat surfaced mirror |
| B. Submarine | b. periscope |
| C. Speed of light in water | a. 2,25,000 ms2 |
| D. Speed of light in diamond | c. 1,24,000 ms2 |
G Define :
Question 1.
Reflection
Answer:
The coming back of light in a medium after striking the surface of some, other medium is called reflection of light.
Question 2.
Plane
Answer:
A flat or fully levelled surface is called plane.
Question 3.
Angle of reflection
Answer:
Angle between the normal and the reflected ray made at the point of incidence is called angle of reflection.
Question 4.
Primary colour
Answer:
The group of Red (R), Green (G) and Blue (B) colours from which all other colours can be had by mixing are called primary colours.
Question 5.
Secondary colour
Answer:
Colours obtained after mixing any two primary colours are called secondary colours.
H. Answer in a few words (not more than one sentence)
Question 1.
Which of the two reflects light much better –
(i) light colours or
(ii) dark colours.
Answer:
Light colours reflects light much better than the dark colours.
Question 2.
Why do microscopes use plane mirrors?
Answer:
Microscopes have plane mirrors to reflect light on the slides to be viewed.
Question 3.
State first law of reflection.
Answer:
The angle of incidence is always equal to angle of reflection.
Question 4.
Write any one characteristic of image formed by a plane mirror.
Answer:
Size of the image is equal to the size of the object.
ICSE Class 7 Physics Important Questions