Ray Optics and Optical Instruments — DPP 1

20 NEET questions from Ray Optics and Optical Instruments, with answers and explanations. Attempt it as a timed test to get scoring, accuracy breakdown and mistake tracking.

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1
A tall man of height 6 feet, want to see his full image. Then required minimum length of the mirror will be :-
  1. A 12 feet
  2. B 3 feet
  3. C 6 feet
  4. D Any length
Show answer & explanation

Correct answer: B

Required minimum length of the mirror = $\frac{H}{2}=\frac{6}{2}=3$ feet
2
Two plane mirrors are at $45 ^ { \circ }$ to each other. If an object is placed between them then the number of images will be
  1. A 5
  2. B 9
  3. C 7
  4. D 8
Show answer & explanation

Correct answer: C

$\mathrm{n}=\frac{360^{\circ}}{\theta}=\frac{360^{\circ}}{45}=8$
n is even so number of images = (n – 1) = 7
3
The colour are characterised by which of following character of light-
  1. A Frequency
  2. B Amplitude
  3. C Wavelength
  4. D Velocity
Show answer & explanation

Correct answer: A

Frequency depend upon the source
4
A ray is incident at $30 ^ { \circ }$ angle on plane mirror. What will be deviation after reflection from mirror.
  1. A $120 ^ { \circ }$
  2. B $60 ^ { \circ }$
  3. C $30 ^ { \circ }$
  4. D $45 ^ { \circ }$
Show answer & explanation

Correct answer: A

$\begin{array}{l}\delta=180-2 \mathrm{i} \\ \delta=180-2 \times 30^{\circ} \\ \delta=120^{\circ}\end{array}$
5
A man is 180 cm tall and his eyes are 10 cm below the top of his head. In order to see his entire height right from toe to head, he uses a plane mirror kept at a distance of 1 m from him. The minimum length of the plane mirror required is
  1. A 180 cm
  2. B 90 cm
  3. C 85 cm
  4. D 170 cm
Show answer & explanation

Correct answer: B

Minimum length of plane mirror required = $\frac{H}{2}=\frac{180}{2}=90 \mathrm{~cm}$
6
A diminished virtual image can be formed only in
  1. A Plane mirror
  2. B A concave mirror
  3. C A convex mirror
  4. D None
Show answer

Correct answer: C

7
The focal length of a concave mirror is 12 cm. Where should an object of height 4 cm be placed, so that a real image of 1 cm height is formed?
  1. A 48 cm
  2. B 3 cm
  3. C 60 cm
  4. D 15 cm
Show answer & explanation

Correct answer: C

$m=\frac{-1}{4} ; m=\frac{f}{f-u} ;-\frac{1}{4}=\frac{-12}{-12-u}$
u = –60 cm
8
When a ray of light is incident normally on a plane mirror then the angle of reflection will be
  1. A $0 ^ { \circ }$
  2. B $90 ^ { \circ }$
  3. C $180 ^ { \circ }$
  4. D $- 90 ^ { \circ }$
Show answer & explanation

Correct answer: A

$\begin{array}{l}\angle \mathrm{i}=\angle \mathrm{r} \\ \because \angle \mathrm{i}=0, \quad \therefore \angle \mathrm{r}=0\end{array}$
9
A square of side 3 cm is placed at a distance of 25 cm from a concave mirror of focal length 10 cm . The centre of the square is at the axis of the mirror and the plane is normal to the axis. The area enclosed by the image of the wire is -
  1. A $4 \mathrm {~cm} ^ { 2 }$
  2. B $6 \mathrm {~cm} ^ { 2 }$
  3. C $16 \mathrm {~cm} ^ { 2 }$
  4. D $36 \mathrm {~cm} ^ { 2 }$
Show answer & explanation

Correct answer: A

Ray Optics and Optical Instruments – NEET-20835
10
An object of height 7.5 cm is placed in front of a convex mirror of radius of curvature 25 cm at a distance of 40 cm. The height of the image should be-
  1. A 2.3 cm
  2. B 1.78 cm
  3. C 1 cm
  4. D 0.8 cm
Show answer & explanation

Correct answer: B

R = 25 cm
f = 12.5 cm
$\begin{array}{l}\mathrm{m}=\frac{\mathrm{f}}{\mathrm{f}-\mathrm{u}}=\frac{12.5}{12.5-(-40)} \\ \mathrm{m}=0.23 \\ \mathrm{~m}=\frac{\text { height of image }}{\text { height of object }}\end{array}$
height of image = 0.23 × 7.5 = 1.78
11
The focal length of a spherical mirror is :-
  1. A Maximum for red light
  2. B Maximum for blue light
  3. C Maximum for white light
  4. D Same for all lights
Show answer & explanation

Correct answer: D

Focal length of spherical mirror does not depend on wavelength of light.
12
The focal length of a convex mirror is 20 cm its radius of curvature will be
  1. A 10 cm
  2. B 20 cm
  3. C 30 cm
  4. D 40 cm
Show answer & explanation

Correct answer: D

R = 2f; R = 2 × 20 = 40 cm
13
A ray gets successively reflection from two mirrors inclined at an angle of $40 ^ { \circ }$. If the angle of incidence on the first mirror is $30 ^ { \circ }$ then the net deviation of this ray after two reflections.
  1. A $40 ^ { \circ }$
  2. B $280 ^ { \circ }$
  3. C $90 ^ { \circ }$
  4. D $240 ^ { \circ }$
Show answer & explanation

Correct answer: B

δ = 360° – 2θ (for two deviation)
δ = 360° – 2 × 40°
δ = 280°
14
A man runs towards stationary plane mirror at a speed of 15 m/s. What is the speed of his image with respect to mirror :-
  1. A 7.5 m/s
  2. B 15 m/s
  3. C 30 m/s
  4. D 45 m/s
Show answer & explanation

Correct answer: B

V$_{I}$ = V$_{0}$, (with respect ot mirror)
V$_{I}$ = 15 m/s
15
Two plane mirrors are lying perpendicular to each other, there is lamp in between mirrors. Then number of images of lamp will be
  1. A 3
  2. B 4
  3. C 5
  4. D 6
Show answer & explanation

Correct answer: A

n = $\frac{360}{90}$ = 4 (even number)
No. of images = 4 – 1 = 3
16
An object of height 1.5 cm is situated at a distance of 15 cm from a concave mirror. The concave mirror forms its real image of height 3.0 cm. The focal length of concave mirror will be
  1. A -10 cm
  2. B -20 cm
  3. C 20 cm
  4. D 30 cm
Show answer & explanation

Correct answer: A

Ray Optics and Optical Instruments – NEET-20838
17
Figure shows two plane mirrors parallel to each other and an object O placed between them. Then the distance of the first three images from the mirror $\mathrm { M } _ { 2 }$ will be :(in cm)
Ray Optics and Optical Instruments – NEET-20828
  1. A 5, 10, 15
  2. B 5, 15, 30
  3. C 5, 25, 35
  4. D 5, 15, 25
Show answer & explanation

Correct answer: C

Ray Optics and Optical Instruments – NEET-20828 then ans. will be 5 cm, 25 cm, 35 cm
18
The focal length of a concave mirror is 50 cm. where an object be placed so that its image is two times magnified, real and inverted -
  1. A 75 cm
  2. B 72 cm
  3. C 63 cm
  4. D 50 cm
Show answer & explanation

Correct answer: A

$m=\frac{f}{f-u}$
m = –2, → Real, Inverted
$-2=\frac{-50}{-50-u} ; u=-75 \mathrm{~cm}$
19
A point object is placed at a distance of 10 cm and its real image is formed at a distance of 20 cm from a concave mirror. If the object is moved by 0.1 cm towards the mirror, the image will shift by about.
  1. A 0.4 cm away from the mirror
  2. B 0.4 cm towards the mirror
  3. C 0.8 cm away from the mirror
  4. D 0.8 cm towards the mirror
Show answer & explanation

Correct answer: A

u = –10 cm, v = –20 cm
$\begin{array}{l}m=-\frac{v}{u} \Rightarrow \frac{-(-20)}{-10}=-2 \\ d v=-m^{2} \times d u \\ \Rightarrow \quad \Delta v=-4 \times 0.1 \\ \Rightarrow \quad \Delta v=-0.4 \mathrm{~cm}\end{array}$
–ve sign indicate object and image are moving opposite to each other.
20
A convex mirror has a radius of curvature of 22 cm. If an object is placed 14 cm away from the mirror then its image is formed at-
  1. A 6.2 cm on the front side of the mirror
  2. B 6.2 cm on the back side of the mirror.
  3. C 51.3 cm on the front of the mirror.
  4. D 51.3 cm on the back side of the mirror.
Show answer & explanation

Correct answer: B

Ray Optics and Optical Instruments – NEET-20843

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