class 10 ch 4 of physics important question

Access very helpful blog  Solutions Class 10 Physics Chapter 4 Solutions

Page No: 173

Very Short Answer Type Questions

Q1. What happens when a ray of light falls normally on the surface of a plane mirror?

Answer:

When a ray of light falls normally on the surface of a plane mirror, the angle of incidence is 0 degrees. From laws of reflection we know that angle of incidence is equal to the angle of reflection. Therefore, the angle of reflection will also be zero. Therefore, the light travels back in the same path.

Q2. A ray of light is incident on a plane mirror at an angle of 30 degrees. What is the angle of reflection?

Answer:

We know from the laws of reflection that the angle of incidence is equal to the angle of reflection. Therefore, angle of reflection will be equal to 30 degrees.

Q3. A ray of light strikes a plane mirror at an angle of 40 degrees to the mirror surface. What will be the angle of reflection?

Answer:

The angle to the mirror surface = 40 degrees

The angle of incidence = 90-40 = 50 degrees

Therefore, angle of reflection = 50 degrees from laws of reflection.

Q4. A ray of light is incident normally on a plane mirror. What will be the:

a) angle of incidence

b) angle of reflection?

Answer:

a) 0 degree

b) 0 degree

Q5. What type of image is formed:

a) in a plane mirror

b) on a cinema screen

Answer:

a) Virtual image

b) Real image

Q6. What kind of mirror is required for obtaining a virtual image of the same size as the object?

Answer:

Plane mirror is required.

Q7. What is the name of the phenomenon in which the right side of an object appears to be the left side of the image in a plane mirror?

Answer:

This phenomenon is known as lateral inversion.

Q8. Name the phenomenon responsible for the following effect:

When we sit in front of a plane mirror and write with our right hand, it appears in the mirror that we are writing with the left hand.

Answer:

This phenomenon is known as lateral inversion.

Q9. If an object is placed at a distance of 10cm in from of a plane mirror, how far would it be from its image?

Answer: 

The image is formed behind the mirror at the distance which is equal to the distance at which the object is placed.

Given,

Distance between object and mirror = 10cm

Distance between mirror and image = 10cm

Therefore, the distance between object and image = 20cm

Q10. Which property of light makes a pencil cast a shadow when it is held in front of a light source?

Answer:

Light travels in a straight line.

Q11. The image seen in a plane mirror cannot be formed on a screen. What name is given to this type of image?

Answer:

Such images are known as virtual images.

Q12. Fill in the blanks:

When light is reflected, the angles of incidence and reflection are ……

Answer:

Equal

Q13. State whether the following statement is true or false:

A student says that we can see an object because light from our eyes is reflected back by the object.

Answer:

False.

Q14. Where is the image when you look at something in a mirror?

Answer:

At the back side of the mirror.

Q15. A ray of light strikes a plane mirror such that its angle of incidence is 30 degree. What angle does the reflected ray make with the mirror surface?

Answer:

Given,

Angle of incidence = 30 degrees

We know that, angle of incidence = angle of reflection from laws of reflection.

Therefore, angle of reflection = 30 degree

Short Answer Type Questions

Q16. What is the difference between a real image and a virtual image?

Give one example of each type of image.

Answer:

The difference between a real image and a virtual image is that real image can be obtained on the screen while the virtual image cannot be obtained on the screen.

Example of real image: image formed on the screen in cinemas.

Example of virtual image: image formed by the plane mirror.

Q17. The letter F is placed in front of a plane mirror:

a) How would its image look when seen in a plane mirror?

b) What is the name of the phenomenon involved?

Answer:

a)

b) Lateral inversion.

Q18. What is lateral inversion? Explain by giving a suitable example.

Answer:

When an object is placed in front of a plane mirror, the image obtained on the appears to on that opposite that is right side appears to be on the left side. This change in the sides of an object and its mirror image is known as lateral inversion.

Example:

Q19. Write the word AMBULANCE as it would appear when reflected in a plane mirror. Why sometimes written in this way on the front of an ambulance?

Answer:

Ambulance is written like the above because when it appears on the rear-view mirror of the vehicle in front can read it the right way because of lateral inversion and make way for it.

Q20. What are the important difference between looking at a photograph of your face and looking at yourself in a plane mirror?

Answer:

The difference between looking at a photograph and looking at yourself is that of lateral inversion. But this doesn’t happen in photographs.

Q21. a) A wall reflects light and a mirror also reflects light. What difference is there in the way they reflect light?

b) Which type of reflection of light leads to the formation of images?

Answer:

a) A wall has a rough surface therefore, when a parallel beam of light falls on it the reflection would be diffused reflection while the surface of the mirror is smooth and the reflection would be regular reflection.

b) Regular reflection.

Q22. What is the difference between regular reflection of light and diffuse reflection of light? What type of reflection of light takes place from:

a) a cinema screen

b) a plane mirror

c) a cardboard

d) still water surface of a lake

Answer:

In regular reflection, the light beams travel parallel to each other and gets reflected in a similar manner while in diffused reflection, the parallel beam of light gets reflected in all the directions.

a) Regular reflection

b) Regular reflection

c) Diffuse reflection

d) Regular reflection

Q23. What can you see in a completely dark room? If you switch on an electric bulb in this dark room as a light source, explain how you could see:

a) the electric bulb

b) a piece of white paper

Answer:

When we are in a completely dark room, we cannot see anything as there is no light.

a) We can see the electric bulb emitting light

b) White paper is visible it reflects the light back that is falling from the electric bulb

Q24. a) A boy with a mouth 5cm wide stands 2m away from a plane mirror. Where is his image and how wide is the image of his mouth?

b) The boy walks towards the mirror at a speed of 1m/s. At what speed does his image approach him?

Answer:

a) The width of the image of the mouth of the boy is 5cm and the image is formed at 2m behind the mirror.

b) The speed of the boy approaching the mirror will be the same as the image approaching = 1m/s

therefore, the speed = 2+2 = 4 m/s.

Q25. a) An extended object in the form of an arrow pointing upward has been placed in front of a plane mirror. Draw a labelled ray diagram to show the formation of its image.

b) State the uses of plane mirror.

Answer:

a)

b) Uses of plane mirrors:

i) It is used for making periscopes.

ii) Used in homes to see ourselves.

iii) Can be used a decorative piece. 

Long Answer Type Questions

Q26. What is meant by reflection of light? Define the following terms used in the study of reflection of light by drawing a labelled ray diagram.

a) incident ray

b) point of incidence

c) normal

d) reflected ray

e) angle of incidence

f) angle of reflection

Answer:

Reflection of light is the phenomenon in which the light ray bounces back from the surface.

a) Incident ray: The light ray that falls on the mirror.

b) Point of incidence: The point at which the incident ray falls.

c) Normal: The line which is at right angle to the mirror.

d) Reflected ray: The light ray that travels back from the mirror.

e) Angle of incidence: The angle made by the incident ray with the normal at the point of incidence.

f) Angle of reflection: The angle made by the reflected ray with the normal at the point of incidence.

Q27. State and explain the laws of reflection of light at a plane surface with the help of a labelled ray diagram. Mark the angle of incidence and reflection clearly on the diagram, if the angle of reflection is 47.5 degrees what will be the angle of incidence?

Answer:

Laws of reflection:

a) The incident ray, the reflected ray, and the normal are in the same plane.

b) The angle of incidence is equal to the angle of reflection.

It is given that the angle of reflection is 47.5 degrees and we know that the angle of incidence is equal to the angle of reflection. Therefore, the angle of incidence is 47.5 degrees.

Q28. With the help of a labelled ray diagram, describe how a plane mirror forms an image of a point source of light placed in front of it. State the characteristics of the image formed in a plane mirror.

Answer:

Below is the ray diagram of an image formed on a plane mirror when the source of light is placed in front of it. Consider a point source of light O which is placed in front of a mirror MM’. OA is the incident ray and AX is the reflected ray. The other ray is OB coming from O after striking the mirror at point B. BY is the reflected ray. Both AX and BY are the reflected rays which meet at point I behind the mirror.

Characteristics of image formed by a plane mirror:

a) The image obtained is laterally inverted.

b) The image obtained is virtual.

c) The image formed is erect.

d) The distance between the object and the image is the same,

e) The size of the image is same as that of the object.

Q29. a) Explain why though both a plane mirror and a sheet of paper reflect light but we can see the image of our face in a plane mirror but not in a sheet of paper.

b) The image in a plane mirror is virtual and laterally inverted. What does this statement mean?

c) Write all the capital letters of the alphabet which look the same in a plane mirror.

Answer:

a) We can see the image of our face on a plane mirror but not in a sheet of paper because on the plane mirror the image is formed after the reflection which is known as regular reflection while image formed on a sheet of paper is known as diffused reflection.

b) The images formed on the plane mirror are always lateral and virtual and cannot be obtained on a screen and is reverse sideways.

c) A, H, I, M, O.

Multiple Choice Questions

Q30. The angle of reflection is equal to the angle of incidence:

a) always

b) sometimes

c) under special conditions

d) never

Answer:

The correct option is a) always

Q31. The angle between an incident ray and the plane mirror is 30 degree. The total angle between the incident ray and reflected ray will be:

a) 30 degree

b) 60 degree

c) 90 degree

d) 120 degree

Answer:

The correct option is d) 120 degree

Q32. A ray of light is incident on a plane mirror making an angle of 90 degree with the mirror surface. The angle of reflection for this ray of light will be:

a) 45 degree

b) 90 degree

c) 0 degree

d) 60 degree

Answer:

The correct option is c) 0 degree

Q33. The image of an object formed by a plane mirror is:

a) virtual 

b) real

c) diminished

d) upside-down

Answer:

The correct option is a) virtual

Q34. The image formed by a plane mirror is:

a) virtual, behind the mirror, and enlarged

b) virtual, behind the mirror, and of the same size as the object

c) real, at the surface of the mirror, and enlarged

d) real, behind the mirror, and of the same size as the object

Answer:

The correct option is b) virtual, behind the mirror, and of the same size as the object

Q35. The figure given alongside shows the image of a clock as seen in a plane mirror. The correct time is:

a) 2.25

b) 2.35

c) 6.45

d) 9.25

Answer:

The correct option is d) 9.25