Light: Selina Exercise 5 Questions and Answers
Understand sources of light, transparent and opaque materials, rectilinear propagation, pinhole cameras, shadows, eclipses and every exercise answer through interactive learning.
What you will learn
Natural and artificial sources, luminous and non-luminous bodies.
Transparent, translucent and opaque media.
Straight-line travel of light and the pinhole camera.
Umbra, penumbra, solar eclipse and lunar eclipse.
Explore how materials transmit light
Select a material type to see what happens to the light beam.
Luminous body
A body that emits its own light, such as the Sun or a glowing bulb.
Non-luminous body
A body seen by reflected light, such as the Moon or a table.
Rectilinear propagation
Light travels in straight lines through a uniform transparent medium.
Shadow
A dark region formed when an opaque object blocks light.
See how distance changes shadow size
Move the slider to place the screen farther from the object.
As the screen moves away, the shadow becomes larger.
Objective Type Questions
Choose one answer for every question, then check your score.
The natural source of light is:
The formation of an inverted image in a pinhole camera shows that:
The luminous body is:
Umbra is a region of:
Penumbra is a region of:
A solar eclipse occurs on:
A lunar eclipse occurs on:
Grease paper is an example of a:
The shadow of an object does not show:
We do not get a shadow when:
Fill in the blanks
Think of the missing word, then open the card to reveal the answer.
1. Light gives us the sensation of ______.
Answer: vision
2. The Sun is a ______ source of light.
Answer: natural
3. A medium through which light cannot pass is called an ______ medium.
Answer: opaque
4. A medium which allows light to pass through it easily is called a ______ medium.
Answer: transparent
5. The Moon is a ______ body.
Answer: non-luminous
6. Light travels in a ______ path.
Answer: straight-line
7. In a pinhole camera, the image formed is ______ and ______.
Answer: real; inverted
8. The darkest portion of a shadow is called the ______.
Answer: umbra
9. The less dark portion of a shadow is called the ______.
Answer: penumbra
10. A lunar eclipse occurs when ______ comes between the Moon and the Sun.
Answer: Earth
True or False
Decide first, then reveal the explanation.
1. The Moon is a natural source of light.Reveal
2. The Moon is self-luminous.Reveal
3. We can see an object through an opaque medium.Reveal
4. Light passes through clear glass.Reveal
5. Light travels in a straight-line path in a uniform medium.Reveal
6. The image formed in a pinhole camera is real.Reveal
7. The image in a pinhole camera gets blurred if the hole is made bigger.Reveal
8. A shadow is formed because light travels in straight lines.Reveal
9. A solar eclipse occurs when the Sun comes between Earth and the Moon.Reveal
10. If Earth's shadow falls on the Moon, the eclipse is called a lunar eclipse.Reveal
Match the following
| Column A | Correct match from Column B |
|---|---|
| Wooden block | Opaque body |
| Sun | Luminous body |
| Umbra | Complete dark part |
| Eclipse | Rectilinear propagation of light |
| Solar eclipse | New moon day |
Short Answer Type Questions
Open each question to read a clear, scientifically checked answer.
Question 1What is light? Define it.
Light is a form of energy that produces the sensation of vision when it enters our eyes.
Question 2How does light make an object visible?
An object becomes visible when light emitted by it, or reflected from it, reaches our eyes.
Question 3Name two natural sources of light.
The Sun and a firefly are natural sources of light.
Question 4List two artificial sources of light.
An electric tube light and a burning candle are artificial sources of light.
Question 5Differentiate between luminous and non-luminous bodies. Give two examples of each.
| Luminous bodies | Non-luminous bodies |
|---|---|
| Emit their own light. | Do not emit their own light. |
| Seen when their emitted light reaches our eyes. | Seen when light from another source reflects from them into our eyes. |
| Examples: Sun, glowing electric bulb. | Examples: Moon, Earth. |
Question 6Is the Moon a luminous object?
No. The Moon has no light of its own; it is visible because it reflects sunlight.
Question 7What do we call a body that shines by its own light?
A body that produces and emits its own light is called a luminous body.
Question 8What do we call an electric bulb producing light?
It is an artificial source of light and, while glowing, a luminous body.
Question 9What is a transparent medium? Give two examples.
A transparent medium allows light to pass through it easily so objects can be seen clearly through it. Examples include clear glass and clean water.
Question 10What do we call a substance through which light cannot pass? Give an example.
It is called an opaque substance. Examples include a wooden block and a metal sheet.
Question 11What do we call a substance through which light passes? Give an example.
A substance that lets light pass through clearly is called transparent. Clear glass is an example.
Question 12Can a transparent medium form an image? Explain your answer.
Yes, under suitable conditions. A transparent lens can form an image by refracting light. A plain transparent sheet, however, does not normally focus light to form a sharp image on a screen.
Question 13How can you obtain a point source of light?
Place a screen with a very fine hole in front of a luminous source, or place the source inside a box with a tiny hole in one side.
Question 14Define a ray of light and a beam of light.
Beam of light: A collection of light rays travelling together.
Question 15What is meant by rectilinear propagation of light?
The travel of light in straight lines through a uniform transparent medium is called rectilinear propagation of light.
Question 16In which arrangement can you see a bulb: through a straight straw or a bent straw? Explain.
The bulb can be seen through a straight straw because light travels in straight lines and reaches the eye. It cannot be seen through a bent straw because the light cannot follow the bend.
Question 17Name a simple application of rectilinear propagation of light.
A pinhole camera is a simple application of rectilinear propagation of light.
Question 18State two factors that affect the size of the image formed in a pinhole camera.
The image size depends mainly on: (1) the distance between the pinhole and the screen, and (2) the distance between the object and the pinhole.
Question 19Is the image obtained in a pinhole camera erect or inverted? Give a reason.
It is inverted. Rays from the top of the object pass through the pinhole and reach the lower part of the screen, while rays from the bottom reach the upper part.
Question 20How is the image affected if another fine hole is made near the first pinhole?
A second image is formed. If the holes are close, the two images overlap and the result appears blurred.
Question 21State the effect on the image if: (a) the hole is made bigger, (b) the object moves toward the pinhole, and (c) the screen moves farther from the pinhole.
- Bigger hole: the image becomes brighter but less sharp or blurred.
- Object closer to pinhole: the image becomes larger.
- Screen farther from pinhole: the image becomes larger, although it may become dimmer.
Question 22What is a shadow? Why is it formed?
A shadow is a dark region formed on a surface when an opaque object blocks light. It forms because light travels in straight lines.
Question 23State two differences between umbra and penumbra.
| Umbra | Penumbra |
|---|---|
| No light from the source reaches this region. | Only part of the light from an extended source reaches this region. |
| It is completely dark. | It is partially dark or dim. |
Question 24Why do birds flying high in the sky usually not cast visible shadows on the ground?
The Sun is an extended source. For a small bird high above the ground, the full dark umbra may end before reaching Earth, while the penumbra spreads out and becomes too faint to notice.
Question 25Why are shadows at noon shorter than in the morning or evening?
Around noon the Sun is higher in the sky, so its rays fall more vertically. The horizontal length of the shadow is therefore shorter.
Question 26What is an eclipse? Name its two main types.
An eclipse occurs when one celestial body moves into the shadow of another or blocks its light from an observer. The two main types studied here are solar eclipse and lunar eclipse.
Question 27When does a lunar eclipse take place? Does it occur on every full moon night?
A lunar eclipse occurs when Earth comes between the Sun and Moon, causing Earth's shadow to fall on the Moon. It does not happen at every full moon because the Moon's orbit is tilted, so exact alignment does not occur each month.
Question 28When does a solar eclipse take place? Does it occur on every new moon day?
A solar eclipse occurs when the Moon comes between the Sun and Earth and its shadow falls on Earth. It does not happen at every new moon because the Moon's orbit is tilted, so exact alignment does not occur each month.
Long Answer Type Questions
Use the diagrams and step-by-step explanations for revision.
Question 1Explain the difference between transparent, translucent and opaque media. Give two examples of each.
| Transparent | Translucent | Opaque |
|---|---|---|
| Allows most light to pass through. | Allows only part of the light to pass through. | Does not allow light to pass through. |
| Objects are seen clearly through it. | Objects appear blurred or faint through it. | Objects cannot be seen through it. |
| Examples: clear glass, clean water. | Examples: tracing paper, frosted glass. | Examples: wood, metal sheet. |
Question 2Describe an experiment to show that light travels in a straight line.
- Place a lighted candle safely on a table.
- Look at the flame through a straight drinking straw with one eye.
- The flame is visible because the light travels straight through the straw.
- Bend the straw and look again.
- The flame is no longer visible because light does not bend around the curved path.
Conclusion: Light travels in a straight line through a uniform medium.
Question 3What is a pinhole camera? Show the formation of an image.
A pinhole camera is a simple camera without a lens. It consists of a light-tight box with a tiny hole on one side and a screen on the opposite side. Light travels through the hole and forms a real, inverted image on the screen.
Question 4Explain the formation of the image of a luminous object in a pinhole camera.
Let the top and bottom of the object be A and B. A ray from A travels through the tiny hole and reaches the lower point A prime on the screen. A ray from B reaches the upper point B prime. Since the rays cross at the pinhole, the image is upside down. The image is real because it can be formed on the screen.
The image size increases when the screen is moved farther from the pinhole or when the object is moved closer to the pinhole.
Question 5Show the formation of the shadow of an opaque object by a point source. What happens if the screen moves away?
For a point source, the opaque object blocks a cone of light and forms a sharp, dark shadow. If the screen is moved farther from the object, the shadow becomes larger because the boundary rays continue to diverge.
Question 6Draw a ray diagram to show the formation of umbra alone.
A point source produces only a sharply bounded umbra.
Question 7Draw a ray diagram to show the formation of umbra and penumbra.
An extended source produces a central umbra surrounded by a lighter penumbra.
Question 8State the conditions under which only penumbra is obtained on the screen.
Only penumbra is obtained when the complete umbra ends before reaching the screen. This can happen when:
- The source is extended rather than a point source.
- The source is larger than the opaque object.
- The object is close to the source.
- The screen is far enough behind the object to lie beyond the tip of the umbral cone.
Question 9How should rays be drawn to form umbra and penumbra on a screen?
Draw boundary rays from the top and bottom edges of the extended source so that they just touch the top and bottom edges of the opaque object. The inner pair encloses the umbra, while the regions between inner and outer boundary rays form the penumbra.
Question 10Draw and explain the formation of a lunar eclipse.
A lunar eclipse occurs at full moon when Earth lies between the Sun and Moon and the Moon enters Earth's shadow.
Question 11Draw and explain the formation of a solar eclipse.
A solar eclipse occurs at new moon when the Moon lies between the Sun and Earth and the Moon's shadow falls on Earth.
Question 12What is an annular solar eclipse? Explain its formation.
An annular solar eclipse occurs when the Moon passes directly in front of the Sun but appears slightly smaller than the Sun because it is relatively farther from Earth. The Moon covers the central part of the Sun, leaving a bright ring called an annulus visible around it.
The bright ring is not the solar corona. The corona is most clearly seen during a total solar eclipse.
Think and Answer
Question 1In a Moon-phase diagram, which position represents the new moon?
The new moon is the position where the Moon lies between Earth and the Sun, with its illuminated half facing away from Earth. In the supplied exercise, this is Box D.
Question 2Can an object have more than one shadow? Give reasons.
Yes. More than one shadow can form when two or more light sources shine on the object from different directions. Each source creates its own shadow. The shadows can differ in direction, darkness and sharpness depending on the positions, sizes and brightness of the sources.
Remember these six ideas
We see an object when light from it reaches our eyes.
The Sun is luminous; the Moon is non-luminous.
Transparent materials transmit most light.
Light travels in straight lines in a uniform medium.
Umbra is fully dark; penumbra is partly dark.
Solar eclipse: Moon in the middle. Lunar eclipse: Earth in the middle.
Light Class 6 Physics FAQ
FAQ 1What is light for Class 6?
Light is a form of energy that produces the sensation of vision when it enters our eyes.
FAQ 2What is rectilinear propagation of light?
It is the property by which light travels in straight lines through a uniform transparent medium.
FAQ 3Why is the image in a pinhole camera inverted?
Rays from the top and bottom of the object cross at the pinhole and reach opposite parts of the screen.
FAQ 4What is the difference between umbra and penumbra?
Umbra is the completely dark part of a shadow, while penumbra is the partially dark part.
FAQ 5Why does a solar eclipse not occur every new moon?
The Moon's orbit is tilted, so the Sun, Moon and Earth are not perfectly aligned at every new moon.
FAQ 6Why does a lunar eclipse not occur every full moon?
The Moon's tilted orbit prevents exact Sun-Earth-Moon alignment at most full moons.
FAQ 7Can a transparent material form an image?
Yes. A transparent lens can form an image by refraction, although a plain transparent sheet does not usually focus light into a sharp image.
FAQ 8What happens when the pinhole is made larger?
The image becomes brighter but less sharp because many overlapping ray bundles reach the screen.
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