CBSE Class 7 Science Light VBQs

Question. A triangular wedge is placed as shown on a flat surface. One of the angles is a right angle as shown.
when seen from DIRECTLY ABOVE IT, what will it look like

(a) A
(b) B
(c) C
(d) D

Answer : B

Question. Galileo, in order to measure the speed of light, performed this simple experiment: He and his assistant each took a lantern that had a shutter in front of it, and stood on hilltops one mile apart in the night. Galileo was to flash his lantern, and the assistant was to open the shutter of his own lantern as soon as he saw the light from Galileo's lantern. Galileo had planned to measure the time taken for light to travel from one hill to the other and back, and calculate the speed of light using the formula, Speed = distance travelled / time taken but he could not measure the speed of light using this method. What could have been the reason for this?

(a) The distance between the two hills was too much for them to see the light from the other person's lantern.
(b) Light does not travel in straight lines and so the distance travelled by it cannot be measured.
(c) The time taken for the light to travel would have been too little to have been measured by them.
(d) Light does not travel because it is present everywhere, so its 'speed' cannot be calculated.

Answer : C

Question. Shown here is an image seen in a microscope, enlarged approximately 100,000 times.  This image could be of

(a) sugar crystals
(b) electrons
(c) blood cells
(d) mustard seeds

Answer : C

Question. A plant was exposed to different intervals of light and darkness to check the flowering of the plant. The table below shows the observations recorded. What can be said about the flowering of the plant based on the data given in the table above?

(a) A minimum duration of darkness is necessary for the plant to flower.
(b) A minimum duration of light is necessary for the plant to flower.
(c) The plant flowers only when exposed to different intervals of light and darkness.
(d) Flowering does not depend on the amount of light or darkness.

Answer : A

Question. Given below is a diagrammatic representation of a solar eclipse. In which of the places shown on earth will a PARTIAL SOLAR ECLIPSE be visible?

(a) A
(b) B
(c) C
(d) D

Answer : C

Question. In a cricket stadium, when the floodlights were switched on at 7pm, multiple shadows of the stumps appeared. The lengths of the shadows of the stumps would have
(a) increased as the match progressed
(b) decreased as the match progressed
(c) first increased and then decreased.
(d) remained the same throughout the match.

Answer : D

Question. Given below is the top view of a mosquito coil. If it is lit at both its ends, at which point will the two lighted ends meet?

(a) A
(b) B
(c) C
(d) D

Answer : C

Question. We see an object?
(a) When it either emits or reflects light.
(b) Only when it reflects light.
(c) Only when it emits light.
(d) When it allows light to pass through itself.

Answer : A

Question. If the word given above is seen in a mirror, it will look like,

Answer : C

Question. The source of energy for the Earth's water cycle is ________.
(a) The wind.    
(b) The sun's radiation.    
(c) The earth's radiation.
(d) The sun's gravity.    

Answer : B

Question. A wet cloth was placed on a balance and left for several days. The change in its mass is shown in the adjacent graph :
What was the mass of water in the cloth at the start of the experiment?

(a) 60 g
(b) 36 g
(c) 24 g
(d) 10 g

Answer : B

Question. The students of a class were given a few substances and asked to classify them as more dense than water or as less dense than water. How should they start?
(a) Find the mass of the substances.
(b) Compare the weight of each substance with the weight of the same volume of water.
(c) Find which of the substances float and which of them sink in water.
(d) Classify the substances according to their shapes.

Answer : C

Question. Which of these absorbs the LEAST sunlight?
(a) forest
(b) ocean
(c) land
(d) Snow

Answer : D

Question. Distilled water is called 'pure' because
(a) It contains dissolved salts.
(b) It boils exactly at 1000C and freezes exactly at 00C.
(c) It contains dissolved oxygen.
(d) It can be produced only in a laboratory.

Answer : B

Question. What is the chemical formula for steam?
(a) CO
(b) H₂O
(c) O₂
(d) (Pure steam does not have a chemical formula.)

Answer : B

Question. Which of the following does not show reflection of light?
a) Plane mirror
b) Concave mirror
c) Convex mirror
d) Card board

Answer : D

Question. Which is used for rear view in cars and other vehicles?
a) Concave mirror
b) Convex mirror
c) Convex lens
d) Concave lens

Answer : B

Question. The image of an object formed by a concave lens is always:
a) Real and diminished
b) Virtual and larger
c) Real and larger
d) Virtual and diminished

Answer : D

Question. The process of splitting of white light in seven colours on passing through a prism is called:
a) Reflection of light
b) Refraction of light
c) Bending of light
d) Dispersion of light

Answer : D

Fill In The Blanks.

(i). An image formed by a plane mirror is always of the same size as that of object.

(ii). In a plane mirror, the left hand of a person appears to be the right hand in the image and right hand appears to be the left hand in the image.

(iii). The image formed by a convex mirror is always virtual and smaller in size.

(iv). Convex lenses are thicker in the middle and concave lenses are thinner in the middle than at the edges.

(v). A prism splits the white light into seven (7) colours.

Write True Or False.

Question. There is reflection of light through a lens.  
Answer : False

Question. The ray of light coming towards the plane mirror is called the reflected ray. 
Answer : False

Question. The image formed by a plane mirror is always in front of the mirror. 
Answer : False

Question. A concave mirror is a part of hollow sphere of glass, whose outer side is coated with silver layer and reflection takes place from the inside.  
Answer : True

Question. Concave lens always forms a virtual, erect and smaller image of the object. 
Answer : True

ACTIVITY- Reflection through a mirror.

Question. The process of change in direction of light after falling on a mirror is called …… of light.
Answer : Reflection.

Question. Angle of incidence is equal to angle of reflection. (True/False)
Answer : True.

ACTIVITY- To obtain the image of an object on a screen using a concave mirror. 

Question. When the object is very far from the concave mirror, the image formed is ……. and ………
Answer : Small and inverted.

Question. The image formed on the screen is real. (True/False)
Answer : True.

Question. For a concave mirror, the image formed is always real. (True/False)
Answer : False.

ACTIVITY- The distance of the object in front of the mirror is same as the distance of the image behind the mirror.

Question. The distance between the object and the mirror is ……. to the distance between the image and the mirror.
Answer : Equal.

Question. The plane mirror has to be placed vertically on the graph paper. (True/False)
Answer : True.

Question. The plane mirror should be vertically upright. (True/False)
Answer : True.

ACTIVITY- To obtain the image of the sun on a wall using a concave mirror. 

Question. The image of the sun formed by the concave mirror on the wall is …….. image.
Answer : Real.

Question. Is the image of a candle seen using a concave mirror same as that of the Sun seen on the wall?
Answer : Yes (both are real).

ACTIVITY-To study the formation of white light by mixing seven colours.

Question. White light is composed of …………. colours.
Answer : Seven (7).

Question. When disc with seven colours is rotated, it appears to be red.. (True/False)
Answer : False.

Question. Name the seven colours of which the white light is made off.
Answer : VIBGYOR- Violet, Indigo, Blue, Green, Yellow, Orange and Red.

ACTIVITY- To obtain the image of the sun on a paper using a convex lens.

Question. The bright spot of light obtained on the paper is the image formed of the ………..
Answer : Sun.

Question. Image obtained on the paper is the virtual image. (True/False)
Answer : False.

ACTIVITY-  To obtain the image of an object on a screen using a convex lens.

Question. The convex lens is placed between the object and the screen. (True/False)
Answer : True.

Question. For a convex lens, image formed is always real. (True/False)
Answer : False.

Match The Column ‘A’ With Column ‘B’.

Answer : (i) - (d), (ii) - (c), (iii) - (b), (iv) - (a), 

Very Short Answer Type Questions.

Question. Which optical instrument uses convex lens?
Answer : Microscope.

Question. Is the image formed by a plane mirror real or virtual?
Answer : Virtual.

Question. What is the seven rainbow coloured disc called?
Answer : Newton disc.

Question. Which lens forms a real image of an object?
Answer : Convex lens.

Short Answer Type Questions.

Question. Differentiate between real and virtual images. Give examples.
Answer : 

Question. A person is standing 5m away from a plane mirror. How far will his image be:
(1) From the mirror, (2) From the person himself?
Answer : (1) From the mirror – 5m, (2) From the person himself – 10m.

Question. Ravi is observing his image in a plane mirror. The distance between the mirror and his image is 6m.
If he moves 2m towards the mirror, then the distance between Ravi and his image will be:
Answer : 8m.

Question. State two differences between convex lens and concave lens.
Answer :

Question. Give two uses of concave mirror.
Answer : Concave mirrors are used in vehicle’s headlights, by ENT doctor and in solar furnaces.

Question. Of how many colours is white light made off? Name them.
Answer : Seven (7). VIBGYOR- Violet, Indigo, Blue, Green, Yellow, Orange and Red.

Long Answer Type Questions.

Question. What is meant by dispersion of light? Explain by using a prism. Which natural phenomenon is associated with dispersion of light?
Answer : Dispersion of light- The process of splitting of white light in seven colours on passing through a prism is called dispersion of light.
When we pass white light through a prism, we see that it splits into seven colours i.e.
VIBGYOR- Violet, Indigo, Blue, Green, Yellow, Orange and Red. Rainbow formed in the sky after raining is due to dispersion of light.

Question. State and explain the characteristics of the image formed by a plane mirror.
Answer : Characteristics of the image formed by a plane mirror-
(1) Plane mirror forms an erect and virtual, image.
(2) Plane mirror forms laterally inverted image.
(3) Plane mirror forms image behind the mirror.
(4) Plane mirror forms the same size image as that of object.
(5) Plane mirror forms image at the same distance from the mirror as the object is in front of it.