The comprehensive approach in SCERT Class 8 Basic Science Textbook Solutions Chapter 12 Spherical Mirrors Important Questions ensure conceptual clarity.
Spherical Mirrors Extra Questions and Answers Class 8 Basic Science Chapter 12 Kerala Syllabus
Spherical Mirrors Class 8 Important Questions
Question 1.
The midpoint of the reflecting surface of a spherical mirror is called the:
a) Centre of Curvature
b) Principal Focus
c) Pole
d) Aperture
Answer:
(c) Pole.
Question 2.
A spherical mirror with a reflecting surface curved inward is called:
a) Convex mirror
b) Concave mirror
c) Plane mirror
d) Aperture
Answer:
(b) Concave mirror.
Question 3.
For a spherical mirror with a small aperture, what is the relationship between focal length (f) and radius of curvature (R)?
a) f = R
b) f = 2R
c) f = \(\frac{R}{2}\)
d) f = R/4
Answer:
(c) f = \(\frac{R}{2}\)
Question 4.
Statement 1: In a concave mirror, light rays that fall parallel to the principal axis converge to a particular point on the principal axis after reflection.
Statement 2: In a convex mirror, light rays that fall parallel to the principal axis also converge to a particular point on the principal axis after reflection.
a) Both statements are correct.
b) Only Statement 1 is correct.
c) Only Statement 2 is correct.
d) Both statements are incorrect.
Answer:
b) Only Statement 1 is correct. (Statement 2 is incorrect; in a convex mirror, they appear to diverge from the focus).
Question 5.
Statement 1: Real images are those that can be caught on a screen.
Statement 2: Virtual images are also those that can be caught on a screen.
a) Both statements are correct.
b) Only Statement 1 is correct.
c) Only Statement 2 is correct.
d) Both statements are incorrect.
Answer:
b) Only Statement 1 is correct. (Statement 2 is incorrect; virtual images cannot be caught on a screen).
Question 6.
Complete the table comparing real and virtual images based on the text book.
| Real Image | Virtual Image |
| Inverted | ……….(a)………. |
| ……….(b)………. | Cannot be caught on a screen |
| Formed in front of the mirror | ……….(c)………. |
Answer:
| Real Image | Virtual Image |
| Inverted | (a) Erect |
| (b) Can be caught on a screen | Cannot be caught on a screen |
| Formed in front of the mirror | (c) Formed behind the mirror |
Question 7.
Classify the following applications based on the type of spherical mirror used (Concave mirror / Convex mirror):
(Shaving mirror, Rear-view mirror in vehicles, Dentist’s mirror, Reflectors in street lamps)
Answer:
Concave mirror: Shaving mirror, Dentist’s mirror.
Convex mirror: Rear-view mirror in vehicles, Reflectors in street lamps.
Question 8.
Statement 1: A convex mirror always forms a small and erect image.
Statement 2: The image formed by a convex mirror is a real image.
a) Both statements are correct.
b) Only Statement 1 is correct.
c) Only Statement 2 is correct.
d) Both statements are incorrect.
Answer:
b) Only Statement 1 is correct. (Statement 2 is incorrect; the image is virtual).
Question 9.
Match the following image characteristics to the correct mirror type.
a) Virtual, smaller than the object
b) Virtual, larger than the object
c) Real, smaller than the object
Answer:
a) Convex Mirror
b) Concave Mirror
c) Concave Mirror
Question 10.
Find and correct the error in this statement:
“Magnification is the ratio of the height of the object (ho) to the height of the image (hi).”
Answer:
Error: The ratio is described incorrectly.
Correction: Magnification is the ratio of the height of the image (hi) to the, height of the object (ho).
Question 11.
Find and correct the error in this statement:
“In a flashlight, a convex mirror is used to create a parallel beam of light.”
Answer:
Error: Convex mirror.
Correction: In a flashlight, a concave mirror is used to create a parallel beam of light.
Question 12.
Find and correct the error in this statement:
“When calculating magnification, measurements below the principal axis should be considered positive.”
Answer:Error: Positive.
Correction: Measurements below the principal axis should be considered negative.
Question 13.
Why are convex mirrors used as rear-view mirrors in vehicles instead of plane mirrors?
Answer:
A convex mirror always forms an erect and small image. Because the image is smaller, it provides a much wider field of view than a plane mirror, allowing the driver to see more of the road and traffic behind them.
Question 14.
In a vehicle headlight, the bulb is placed at the principal focus of the concave mirror. Why?
Answer:
This is because light rays that start from the principal focus (F) of a concave mirror travel parallel to the principal axis after reflection. This property is used to send out a strong, parallel beam of light that can travel a long distance.
Question 15.
Why is the warning “OBJECTS IN THE MIRROR ARE CLOSER THAN THEY APPEAR” written on vehicle side mirrors?
Answer:
A convex mirror always forms a small image. This makes the driver feel that the vehicles coming from behind are at a great distance, even when they are not. The warning is there to prevent accidents caused by this misperception.
Question 16.
A concave mirror has a focal length of 15 cm. What is its radius of curvature?
Answer:
f = \(\frac{R}{2}\)
R = 2f
= 2 × 15 = 30 cm
Question 17.
A concave mirror produces an image that is the same size as the object. If the object is placed 40 cm from the mirror, what is the mirror’s focal length?
Answer:
An image of the same size is formed only when the object is placed at the Centre of Curvature (C).
This means the object distance is the Radius of Curvature. So, R = 40 cm Since f = R/2, the focal length f = 40 cm / 2 = 20 cm.
Question 18.
An object with a height of 10 cm is placed in front of a concave mirror. It produces an inverted image with a height of 5 cm. What is the magnification (m)?
Answer:
Height of object (ho) = 10 cm. (This is measured above the axis, so it is positive).
Height of image (hi) = 5 cm. (It is inverted, so it is measured below the axis, making it negative).
Answer:
m = hi / ho
m = -5 cm / 10 cm = -0.5.
Question 19.
Describe a simple procedure to find the approximate focal length of a concave mirror using a distant object (like the sun or a faraway building)
Answer:
- Hold the concave mirror and face it towards a distant object (like the sun).
- Hold a sheet of paper (to act as a screen) in front of the mirror.
- Light rays from a distant object travel parallel to the principal axis.
- Adjust the position of the paper until you get the smallest and sharpest image of the distant object (a bright point if using the sun).
- This image is formed at the principal focus (F).
- Measure the distance from the mirror’s surface (Pole, P) to the paper (F) using a scale. This distance is the focal length (f) of the mirror.
Question 20.
You are given a concave mirror and a convex mirror, but you don’t know which is which. Describe a simple test to identify them by looking at your own image.
Answer:
- Bring your face very close to the first mirror.
- Observe the image.
- If the image is large, erect, and virtual (magnified), it is the Concave Mirror.
- If the image is small, erect, and virtual, it is the Convex Mirror.
- (Alternative) Try to form an image of a distant window on a wall. The mirror that forms a real, inverted image on the wall is the Concave Mirror. The convex mirror cannot form a real image.
Question 21.
Describe the path of a light ray traveling parallel to the principal axis after it reflects from:
a) a concave mirror
b) a convex mirror
Answer:
a) In a concave mirror, a light ray that falls parallel to the principal axis will pass through the principal focus (F) after reflection.
b) In a convex mirror, a light ray that falls parallel to the principal axis will reflect as if it is diverging from the principal focus (F) located behind the mirror.
Question 22.
Complete the table
| NO | Angle of incidence | Angle of reflection |
| 1 | 30° | ……….(a)………. |
| 2 | ……….(b)………. | 40° |
| 3 | 50° | ……….(c)………. |
| 4 | 60° | ……….(d)………. |
Answer:
a. 30°
b. 40°
c. 50°
d. 60°
Question 23.
If the radius of curvature of a concave mirror is 24 cm what is its focal length?
Answer:
R = 24 cm
f = \(\frac{R}{2}\) = \(\frac{24}{2}\) = 12 cm
Question 24.
Find the radius of curvature of a convex mirror of focal length 0.6m
Answer:
f = \(\frac{R}{2}\)
0.6 = \(\frac{R}{2}\) = o.6 × 2 = 1.2 m
Question 25.
Write the characteristics of the image formed by an object placed at the centre of curvature of a concave mirror?
Answer:
Position: At the centre of curvature at the same side
Size: Same as the size of the object Nature: Real, Inverted
Question 26.
Complete the figure
Answer:
Question 27.
Complete the table
| Path of incident Ray | Path of reflected ray | |
| Concave mirror | Convex mirror | |
| Path of incident Ray | ……. a …….. | ……. b ……. |
| Parallel to pricipal axis | …….. c ……. | ……. d ……. |
| Through/to principal focus | …….. e ……. | …….. f …….. |
| Through centre of curvature | …….. g ……. | …….. h ……. |
Answer:
a. Passes through principal focus
b. Seem to come from the principal focus
c, d. Returns parallel to the principal axis
e, f. Returns through the same path
g, h. Reflects in the same angle of incident ray.
Question 28.
Write uses of concave mirrors
Answer:
- As shaving mirror
- As make up mirror
- As head mirrors used by doctors
- In film projectors
Question 29.
Examine the position of the object given in the figure and table the following peculiarities
a. position of the image
b. size of the image
c. nature of the image
Answer:
a. Behind the mirror.
b. Larger than the object.
c. Erect and virtual
Question 30.
Write the uses of convex mirror
Answer:
- As reflector in the street light
- As rear view mirror
- In search lights
Question 31.
Which type of spherical mirror is used as rear view mirror in vehicles?
(concave mirror, convex mirror, plane mirror)
Answer:
Convex
Question 32.
a. Complete the ray diagram of image formation of the object OB placed in front of the mirror.
b. Write two features of the image formed?
Answer:
a. 
b. Virtual, erect and diminished.
Question 33.
Which mirror is called a converging mirror?
(a) Plane Mirror
(b) Concave Mirror
(c) Convex Mirror
(d) Spherical Mirror
Answer:
(b) Concave Mirror
Question 34.
The rear-view mirror in a car is a:
(a) Concave Mirror
(b) Plane Mirror
(c) Convex Mirror
(d) Cylindrical Mirror
Answer:
(c) Convex Mirror
Question 35.
The image formed by a convex mirror is always:
(a) Real and Inverted
(b) Virtual and Magnified
(c) Virtual and Diminished
(d) Real and Diminished
Answer:
(c) Virtual and Diminished
Question 36.
If the Radius of Curvature (R) of a spherical mirror is 50 cm, its focal length (f) is:
(a) 100 cm
(b) 50 cm
(c) 25 cm
(d) 12.5 cm
Answer:
(c) 25 cm (f = R/2 = 50/2)
Question 37.
A concave mirror can form a real, inverted, and same-size image when the object is placed at:
(a) Focus (F)
(b) Centre of Curvature (C)
(c) Pole (P)
(d) Infinity
Answer:
(b) Centre of Curvature (C)
Question 38.
Define the terms Pole (P) and Principal Focus ($F$) for a spherical mirror.
Answer:
Pole (P): The geometrical centre of the spherical mirror’s reflecting surface.
Principal Focus (F): The point on the principal axis where light rays parallel to the principal axis meet (concave) or appear to diverge from (convex) after reflection.
Question 39.
A dentist uses a specific type of spherical mirror.
(a) Name the mirror.
(b) Why is this mirror preferred by dentists?
Answer:
a) Concave Mirror.
b) It forms a magnified, erect, and virtual image of the tooth when held close, allowing the dentist to see details clearly.
Question 40.
Differentiate between a Real Image and a Virtual Image.
Answer:
Real Image: Formed when light rays actually meet after reflection. Can be obtained on a screen. Virtual Image:
Formed when light rays only appear to meet behind the mirror. Cannot be obtained on a screen.
Question 41.
State the two primary reasons why a convex mirror is used as a rear-view mirror in vehicles.
Answer:
A convex mirror is preferred because:
- It always forms an erect (upright) image, which is easier for the driver to interpret.
- It provides a much wider field of view because its reflective surface curves outward, allowing the driver to see more of the surrounding traffic.
Question 42.
A concave mirror is used in a solar furnace. Explain the principle behind this use.
Where must the solar heater coil be placed to get maximum heat?
Answer:
Principle: Concave mirrors are converging mirrors. They take the nearly parallel rays of light coming from the sun (a distant source) and reflect them to converge at a single point.
Placement: The solar heater coil must be placed at the Principal Focus (F) of the concave mirror. This ensures ail the reflected solar energy is concentrated into the smallest possible area, producing maximum heat.
Question 43.
Complete the following table for a Concave Mirror:
| Position of the Object | Position of the image | Characteristics of the Image |
| At Infinity | At F | Highly Diminished, Real, inverted |
| Between C and F | ? | ? |
| Between F and P | ? | Magnified, Erect, Virtual |
Answer:
| Position of the Object | Position of the image | Characteristics of the Image |
| At Infinity | At F | Highly Diminished, Real, inverted |
| Between C and F | Beyond C | Magnified, Real, Inverted |
| Between F and P | Behind the Mirror | Magnified, Erect, Virtual |