11. Light

Give Reasons for the following questions:

Q1.  We should always look at the image of the Sun on a screen or a wall. Why?

Ans:

• We should never look directly towards the Sun or its image as it may damage your eyes.
• Hence, we look at image of the sun on the screen or a wall.

Q2. Why can’t we see anything from a bend pipe?

Ans:

We can’t we see anything from a bend pipe because light travels in a straight line. When the pipe is bent the light can’t reach us and so we can’t see anything.

Q3. Paheli was wiping the wet steel utensils with a cloth to help her mother. While doing so she was surprised how she could see her face in a stainless-steel plate. Help her to understand why so?

Ans:

• Stainless steel plate has a shining surface which acts like a mirror.
•  Light travels in a straight line but can change its direction when it falls on a shining surface.
• This is called as reflection of light due with we can see our image in shining surfaces like mirror, stainless steel plate or spoon and water.

Q4. What type of image is formed on the shiny surface of the new bicycle bell? Why?

Ans:

• The image seen in the shiny surface of a bicycle bell is smaller & erect.
• This is because the surface of the bell is curved outwards and acts like a spherical convex mirror.
• Image produced by a convex mirror is always diminished & erect.

Q5.  In the side mirrors of vehicles the images of all the objects appear smaller than the objects themselves. Why?

Ans:

• The mirrors of side mirrors of vehicles are convex mirrors which are curved outwards.
• They form a virtual, erect & diminished image of objects in front of them. 
• Also, these mirrors can form images of objects spread over a large area which reduces blind spots and improves safety.
• So, this helps the drivers to see the traffic behind them.

Q6. An image of an object in front of a plane mirror cannot be obtained on a screen. Why?

Ans:

• An image formed by a plain mirror is always virtual, erect & laterally inverted.
• A virtual image is an upright image that cannot be obtained on a screen & formed when light rays appear to diverge from a point.

Thus an image of an object in front of plane mirror cannot be obtained on screen.

Q7.  Why not to focus sunlight with a convex lens on any part of your body?

Ans:

• Convex lens converges (concentrate) the light falling on it. Hence it is also called converging lens.
• Thus, a convex lens will converge the sunlight on that part of the body causing high intensity heat which can cause severe burns.

Q8. Soap bubbles appear colourful in sunlight. Why?

Ans:

• When sunlight of white light passes through soap bubbles it splits into seven colours making them appear colourful,
• This phenomenon is called dispersion of light.

Answer the following questions in short:

Q1. What is the meaning of laterally inverted image?

Ans: 

In an image formed by a plain mirror, the left side of the object is seen on the right side in the image and vice-versa.

Q2. What is light?

Ans:

Light is a form of energy that allows us to see.

Q3. What is a virtual image?

Ans:

A virtual image is an upright image that cannot be obtained on a screen & formed when light rays appear to diverge from a point.

Q4. What is a real image?

Ans:

A real image is an inverted image that can be obtained on a screen & is formed when light rays converge at a point.

Q5. What are the types of mirrors?

Ans:

• Mirrors are of two types: plain & spherical.
• Spherical mirror are of two types: convex & concave.

Q6.  Which devices act like a mirror?

Ans:

Devices which act like mirror are:

• Any shining surface stainless steel plate or spoon.
• Water

Q7. What is a concave mirror?

Ans:

A mirror whose reflecting surface is is curved inward is called a concave or converging mirror.

Q8. What is a convex mirror?

Ans:

A mirror whose reflecting surface is is curved outward is called a concave or diverging mirror.

Q9. What are the seven colours of white light?

Ans:

The seven colours are red, orange, yellow, green, blue, indigo and violet.

Q10.  How a convex lens is used as a magnifying glass?

Ans:

A convex lens converges light rays & makes an image appear much larger than that of the object. Hence the object appears magnified.

Answer the following questions:

Q1. What is the difference between real and virtual images?

Ans:

Q2. List the uses of concave mirror.

Ans:

Concave mirror is used:

• By doctors to examine eyes, ears, nose and throat
• By dentists to see an enlarged image of the teeth.
• As reflectors of torches.
• As headlights of cars and scooters.