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06. Light

Answers to textbook exercises

Prepared by: learnloophq@gmail.com

Last edited 26 days ago by Learn LoopHQ.

Chapter: 06. Light

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CONNECT

F I R E

B U L B

S U N

S T A R

CHECK YOUR PROGRESS

The image formed by a pinhole camera is always

a. real.

When the distance between the object and the pinhole is increased, the size of the image

a. decreases.

If the size of the pinhole is increased, the image becomes

c. blurred.

ECO-SOLDIER

How does mercury affect our vision?

Mercury vapour can cause restricted vision and difficulty in recognising the distance between objects.

What impact does mercury vapour have on the environment?

Mercury vapour is a toxic metal that has a strong impact on organs such as the brain, lungs, and kidneys. It also contaminates the environment.

List any two ways through which we can reduce the use of CFLs. Will this help in promoting a safer work environment for labourers? Give reason.

Two ways to reduce CFL use are: 1) Switching to LED bulbs. 2) Promoting government schemes that make LED bulbs affordable.

Yes, this will help promote a safer work environment for labourers because LED bulbs do not contain mercury vapour, thus eliminating the risk of mercury exposure from broken CFLs.

PREPPING FOR PISA

Assertion (A): LEDs emit radiation. Reason ®: LEDs directly convert electricity to light.

d. A is false but R is true.

Based on the information given above, state whether the following statements are true or false.

⁠

CHECK YOUR PROGRESS

Lunar eclipse occurs when the Earth comes

a. between the sun and the moon.

Solar eclipse occurs on

b. a new moon day.

Total solar eclipse occurs at places on the Earth which lie in the

b. umbra region of the moon’s shadow.

EVALUATION A. Choose the correct option.

Which of the following is the main source of light on the Earth?

a. The sun

Which type of objects do not allow light to pass through them?

b. Opaque

An image formed in water is

b. Inverted

Which of the following does not affect the image formed by the pinhole camera?

c. Shape of the pinhole

A lunar eclipse occurs only on a

a. full moon night.

Tina made five holes in a cardboard. She placed a candle in front of the cardboard and stood on the other side. What conclusion would she draw from her observations?

b. Light rays travel in a straight line.

B. Fill in the blanks.

The darkest portion of a shadow is called umbra.

Light travels in a straight line.

A solar eclipse occurs when the moon comes in between the sun and the Earth.

The working of a pinhole camera is based on the property of rectilinear propagation of light.

A shadow is formed when the path of light is obstructed by an opaque object.

C. Write true (T) or false (F) against the following statements. 6. A solar eclipse occurs when the moon comes in between the sun and the Earth. * True 7. An umbra is the partially dark part of a shadow. * False 8. A solar eclipse should be seen with naked eyes. * False 9. A shadow is formed because light travels in a straight line. * True 10. Lunar eclipses occur on every full moon night. * False

D. Name the following:

the principle on which a pinhole camera is based

Rectilinear propagation of light

the partially dark region of a shadow

Penumbra

the eclipse that occurs when the Earth comes in between the sun and the moon

Lunar eclipse

objects that produce their own light

Luminous objects

E. Short answer type questions. 5. Define magnification. * Magnification is the ratio of the size of the image to that of the object. 6. Define the umbra and penumbra regions of a shadow. * Umbra: The central, darkest part of the shadow which does not receive any light from the source. * Penumbra: The region of partial darkness which surrounds the umbra, receiving some light from the source. 7. Write the effects of the shape and size of the pinhole on the formation of image in a pinhole camera. * Shape of the pinhole: The shape of the pinhole does not affect the image formed. * Size of the pinhole: If the size of the pinhole is increased, the image formed will be blurred. 8. What is an eclipse? Name the two types of eclipses. * An eclipse is the shadow cast by the Earth or the Moon when they align with the Sun. * The two types of eclipses are solar eclipse and lunar eclipse.

F. Long answer type questions. 9. What is rectilinear propagation of light? Demonstrate this property with the help of an activity. * Rectilinear propagation of light is the basic property of light travelling in a straight line unless it encounters any object which changes its direction. * Activity Demonstration (using a hollow rubber tube/straw): * Aim: To demonstrate that light travels in a straight line. * Materials required: Burning candle and a hollow rubber tube or a straw. * Procedure: Place the burning candle vertically on a plane surface. Now peep through the straight rubber tube to view the candle flame with one eye, keeping the other eye closed. Then, bend the tube and try to view the flame through it again. * Observation: You will find that in the first case, the flame can be seen clearly. But you cannot see the flame on bending the tube. * Conclusion: This proves that light travels in a straight line. 10. Explain solar and lunar eclipses with diagrams. * Solar Eclipse: A solar eclipse occurs when the Sun, the Moon, and the Earth are in a straight line, and the Moon lies between the Sun and the Earth. The Moon casts its shadow on the Earth, making the Sun partially or wholly invisible from certain regions on Earth. Types include Total, Partial, and Annular solar eclipses, depending on the observer’s position in the Moon’s umbra or penumbra. (Refer to Fig. 6.16 and Fig. 6.17 for diagrams showing alignment and shadow regions.) * Lunar Eclipse: A lunar eclipse occurs when the Sun, the Earth, and the Moon are in a straight line, and the Earth comes in between the Sun and the Moon. The Earth casts its shadow on the Moon, making the Moon partially or wholly invisible from Earth. Types include Total and Partial lunar eclipses, depending on whether the Moon is fully or partially within Earth’s umbra or penumbra. (Refer to Fig. 6.19 for diagrams showing alignment and shadow regions.)

Higher Order Thinking Skills (HOTS)

At which position of the sun would the shadow of the lamp be the shortest?

c. R

When the torch is moved away from the ball, the size of its shadow

b. decreases

Virtual Tour

A pinhole camera forms image without using a ____

lens

In the video what was used to cover the cut face of cardboard box: tracing paper or photographic plate?

tracing paper

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