Mirrors and Lenses Fundamentals Mirror Equation and Magnification Quiz 1

 

Worksheet: Mirrors and Lenses (MCQ)

Part A: Conceptual Questions (1–10)

Q1

A concave mirror forms an image same size as the object when the object is placed at:

A. F
B. Between F and C
C. C
D. Beyond C

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Q2

A convex mirror always forms an image that is:

A. Real and inverted
B. Virtual and inverted
C. Virtual and erect
D. Real and erect

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Q3

Which mirror is used as a rear-view mirror in vehicles?

A. Plane mirror
B. Concave mirror
C. Convex mirror
D. Parabolic mirror

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Q4

If an object is placed between focus and pole of a concave mirror, the image formed is:

A. Real, inverted, magnified
B. Virtual, erect, magnified
C. Real, inverted, diminished
D. Virtual, erect, diminished

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Q5

The focal length of a concave mirror is 15 cm. The radius of curvature is:

A. 7.5 cm
B. 15 cm
C. 30 cm
D. 45 cm

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Q6

Which lens always forms virtual, erect, and diminished images?

A. Convex lens
B. Concave lens
C. Biconvex lens
D. Plano-convex lens

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Q7

The mirror formula is:

A. $\frac{1}{f}=\frac{1}{u}-\frac{1}{v}$
B. $\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$
C. $f=uv$
D. $f=u+v$

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Q8

If magnification of a mirror is +3, the image is:

A. Real and inverted
B. Virtual and erect
C. Real and erect
D. Inverted and diminished

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Q9

If an object is placed at 2F of a convex lens, the image is:

A. At F
B. At 2F
C. Between F and 2F
D. At infinity

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Q10

Magnification for mirrors is given by:

A. $m = -\frac{v}{u}$
B. $m = \frac{v}{u}$
C. $m = \frac{u}{v}$
D. $m = \frac{f}{u}$

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Part B: Numerical MCQs (11–20)

Use

$$\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$$ $$m = -\frac{v}{u}$$

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Q11

An object is placed 30 cm in front of a concave mirror with focal length 15 cm.
Image distance is:

A. −15 cm
B. −30 cm
C. −45 cm
D. +30 cm

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Q12

An object is placed 20 cm from a concave mirror with focal length 10 cm.
The magnification is:

A. −1
B. +1
C. −2
D. +2

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Q13

A convex mirror has focal length 20 cm. An object is placed 40 cm from the mirror.
The image distance is:

A. 13.3 cm
B. 20 cm
C. 40 cm
D. 10 cm

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Q14

An object 4 cm tall is placed 20 cm from a concave mirror of focal length 10 cm.
Height of the image is:

A. −4 cm
B. +4 cm
C. −8 cm
D. +8 cm

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Q15

A convex lens has focal length 10 cm. An object is placed 15 cm from the lens.
Image distance is:

A. 6 cm
B. 10 cm
C. 30 cm
D. 15 cm

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Q16

An object placed 20 cm from a convex lens forms an image 60 cm away.
Focal length is:

A. 10 cm
B. 12 cm
C. 15 cm
D. 20 cm

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Q17

An object is placed 10 cm from a concave lens of focal length 15 cm.
Image distance is:

A. 6 cm
B. 30 cm
C. −6 cm
D. −30 cm

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Q18

A concave mirror produces an image three times the object size. If object distance is 20 cm, the image distance is:

A. 60 cm
B. 30 cm
C. −60 cm
D. −30 cm

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Q19

An object is placed 50 cm from a convex lens of focal length 25 cm.
The image distance is:

A. 25 cm
B. 50 cm
C. 75 cm
D. 100 cm

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Q20

A concave mirror forms an image 40 cm in front of the mirror. If focal length is 20 cm, the object distance is:

A. −20 cm
B. −40 cm
C. −80 cm
D. −60 cm

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Answer Key

Q	Ans
1	C
2	C
3	C
4	B
5	C
6	B
7	B
8	B
9	B
10	A
11	B
12	A
13	A
14	A
15	C
16	C
17	C
18	A
19	B
20	B

Detailed Solutions

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Q11

Given

$$u = -30\text{ cm},\quad f = -15\text{ cm}$$

Mirror formula

$$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$$ $$\frac{1}{-15}=\frac{1}{v}+\frac{1}{-30}$$ $$\frac{1}{v}=-\frac{1}{15}+\frac{1}{30}$$ $$\frac{1}{v}=-\frac{1}{30}$$ $$v=-30\text{ cm}$$

Image at 30 cm in front (real image).

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Q12

Magnification

$$m=-\frac{v}{u}$$

Using mirror formula

$$\frac{1}{-10}=\frac{1}{v}+\frac{1}{-20}$$ $$\frac{1}{v}=-\frac{1}{10}+\frac{1}{20}$$ $$\frac{1}{v}=-\frac{1}{20}$$ $$v=-20\text{ cm}$$
$$m=-\frac{-20}{-20}=-1$$

Image is same size and inverted.

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Q13

Convex mirror

$$f=+20\text{ cm},\quad u=-40\text{ cm}$$
$$\frac{1}{20}=\frac{1}{v}-\frac{1}{40}$$ $$\frac{1}{v}=\frac{1}{20}+\frac{1}{40}$$ $$\frac{1}{v}=\frac{3}{40}$$ $$v=13.3\text{ cm}$$

Virtual image behind mirror.

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Q14

​

Substitute values:

$$\frac{1}{-10} = \frac{1}{v} + \frac{1}{-20}$$ $$\frac{1}{-10} = \frac{1}{v} - \frac{1}{20}$$v=−20 cm

Magnification for mirrors:

$$m = -\frac{v}{u}$$

Substitute values:

$$m = -\frac{-20}{-20}$$ $$m = -1$$

Find image height

$$m = \frac{h_i}{h_o}$$ $$-1 = \frac{h_i}{4}$$ $$h_i = -4 \text{ cm}$$

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Q15

Lens formula

$$\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$$ $$\frac{1}{10}=\frac{1}{v}-\frac{1}{15}$$ $$\frac{1}{v}=\frac{1}{10}+\frac{1}{15}$$ $$\frac{1}{v}=\frac{5}{30}$$ $$v=6\text{ cm}$$

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Q16

$$u=-20,\quad v=60$$
$$\frac{1}{f}=\frac{1}{60}-\frac{1}{-20}$$ $$\frac{1}{f}=\frac{1}{60}+\frac{1}{20}$$ $$\frac{1}{f}=\frac{4}{60}$$ $$f=15\text{ cm}$$

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Q17

$$u=-10,\quad f=-15$$
$$\frac{1}{-15}=\frac{1}{v}+\frac{1}{-10}$$ $$\frac{1}{v}=-\frac{1}{15}+\frac{1}{10}$$ $$\frac{1}{v}=\frac{1}{30}$$ $$v=30\text{ cm}$$

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Q18

Magnification

$$m=3$$
$$m=-\frac{v}{u}$$ $$3=-\frac{v}{-20}$$ $$v=60\text{ cm}$$

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Q19

$$u=-50,\quad f=25$$
$$\frac{1}{25}=\frac{1}{v}-\frac{1}{-50}$$ $$\frac{1}{v}=\frac{1}{25}-\frac{1}{50}$$ $$\frac{1}{v}=\frac{1}{50}$$ $$v=50\text{ cm}$$

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Q20

$$v=-40,\quad f=-20$$
$$\frac{1}{-20}=\frac{1}{-40}+\frac{1}{u}$$ $$\frac{1}{u}=-\frac{1}{20}+\frac{1}{40}$$ $$\frac{1}{u}=-\frac{1}{40}$$ $$u=-40\text{ cm}$$