#### Optics English Medium Free Online Test 1 Mark Questions with Answer Key 2020 - 2021

10th Standard

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Science

Time : 00:15:00 Hrs
Total Marks : 15

Part A

15 x 1 = 15
1. A small bulb is placed at the principal focus of a convex lens. When the bulb is switched on, the lens will produce

(a)

a convergent beam of light

(b)

a divergent beam of light

(c)

a parallel beam of light

(d)

a coloured beam of light

2. Power of a lens is –4D, then its focal length is

(a)

4m

(b)

–40m

(c)

–0.25 m

(d)

–2.5 m

3. Which of the following lens would you prefer to use while reading small letters found in a dictionary?

(a)

A convex lens of focal length 5 cm

(b)

A concave lens of focal length 5 cm

(c)

A convex lens of focal length 10 cm

(d)

A concave lens of focal length 10 cm

4. The group of rays is ______

(a)

lines

(b)

dots

(c)

beam

(d)

none ofthese

5. Velocity and wavelength of light are related by a relation

(a)

g-c⋋

(b)

$\gamma =\frac { c }{ \lambda }$

(c)

c=$\gamma$

(d)

both b & c

6. _____ determines speed of light in a medium.

(a)

thickness

(b)

wavelength

(c)

refractive index

(d)

both b and c

7. When a ray of light travels from one medium to another, it bends. This phenomenon is called.

(a)

reflection

(b)

dispersion

(c)

refraction

(d)

interference

8. Rainbow formation is due to _____ water droplets.

(a)

Ionisation

(b)

absorption of sunlight

(c)

reflection and refraction of sunlight

(d)

reflection of sunlight

9. The scattering of light by colloidal particles is _____  scattering.

(a)

Ray light

(b)

Mie

(c)

Raman

(d)

Tyndall

10. In spherical lenses, all distance are measured from

(a)

optic centre

(b)

principal focus

(c)

principal axis

(d)

centre of curvature

11. According to snell's law

(a)

μ=$\frac { sini }{ sinr }$

(b)

μ =$\frac { { c }_{ a } }{ { c }_{ m } }$

(c)

μ=$\frac { sinr }{ sini }$

(d)

μ=$\frac { { c }_{ m } }{ { c }_{ a } }$

12. The point at which the principal axis meets the surface of the lens is

(a)

centre of curvature

(b)

radius of curvature

(c)

focus

(d)

pole

13. Convex lens forms a highly diminished, real and inverted image, when an object is at

(a)

infinity

(b)

F

(c)

below F & c

(d)

beyond 2 F

14. An object is placed 25 cm from a convex lens whose focal length is 10 cm. The image distance is _______ cm.

(a)

50

(b)

16.66

(c)

6.66

(d)

10

15. The phenomena of light responsible for the working of the human eye is

(a)

Reflection

(b)

Refraction

(c)

Power

(d)

Accommodation