# Free Objective Test 01 Practice Test - 11th and 12th

### Question 1

Refractive index for a material for infrared light is

**[CPMT 1984]**

Equal to that of ultraviolet light

Less than for ultraviolet light

Equal to that for red colour of light

Greater than that for ultraviolet light

#### SOLUTION

Solution :B

### Question 2

A monochromatic beam of light passes from a denser medium into a rarer medium. As a result **[CPMT 1972]**

Its velocity increases

Its velocity decreases

Its frequency decreases

Its wavelength decreases

#### SOLUTION

Solution :A

### Question 3

Monochromatic light is refracted from air into the glass of refractive index The ratio of the wavelength of incident and refracted waves is

**[JIPMER 2000; MP PMT 1996, 2003]**

#### SOLUTION

Solution :C

### Question 4

The refractive index of a certain glass is 1.5 for light whose wavelength in vacuum is 6000 Å. The wavelength of this light when it passes through glass is

**[NCERT 1979; CBSE PMT 1993; ****MP PET 1985, 89]**

4000 Å

6000 Å

9000 Å

15000 Å

#### SOLUTION

Solution :A

### Question 5

The refractive index of a piece of transparent quartz is the greatest for

**[MP PET 1985, 94]**

Red light

Violet light

Green light

Yellow light

#### SOLUTION

Solution :B

### Question 6

The ratio of the refractive index of red light to blue light in air is

**[CPMT 1978]**

Less than unity

Equal to unity

Greater than unity

Less as well as greater than unity depending upon the experimental arrangement

#### SOLUTION

Solution :A

### Question 7

When light is incident on a medium at angle *i* and refracted into a second medium at an angle *r*, the graph of sin *i vs *sin*r* is as shown in the graph. From this, one can conclude that

Velocity of light in the I medium is 1.73 times the velocity in the II medium

#### SOLUTION

Solution :B

### Question 8

In the adjoining diagram, a wavefront *AB*, moving in air is incident on a plane glass surface *XY*. Its position *CD* after refraction through a glass slab is shown also along with the normals drawn at *A* and *D*. The refractive index of glass with respect to air (μ=1 ) will be equal to

#### SOLUTION

Solution :B

in the case of refraction is CD is the refracted waves front and V1 and V2 are the speed of light in

the two media, then in the time the wavelets from B reaches C, the wavelets from A will reach D,

such that

t=BCva=ADvg⇒BCAD=vavg ...(i)

But in △ACB,BC=ACsinθ ...(ii)

While in △ACD,AD= AC sinϕ′ ...(iii)

From equations (i), (ii) and (iii) vavg=sin θsin ϕ′

Also μ∝1v⇒vavg=μgμa=sin θsin ϕ′⇒μg=sinθsinϕ′

### Question 9

On a glass plate a light wave is incident at an angle of 60∘. If the reflected and the refracted waves are mutually perpendicular, the refractive index of material is

#### SOLUTION

Solution :B

From figure r=30∘

∴μ=sinisinr=sin60∘sin30∘=√3

### Question 10

Velocity of light in glass whose refractive index with respect to air is 1.5 is 2×108m s−1 and in certain liquid the velocity of light found to be 2.50×108m s−1.The refractive index of the liquid

with respect to air is

#### SOLUTION

Solution :C

Refractice index of glass slab =1.5

Velocity of light in glass =2×108m s−1

Velocity of light in liquid =2.50×108m s−1

μα1v⇒μliμg=vgvl⇒μl1.5=2×1082.5×108

⇒μl=1.2

### Question 11

A ray of light is incident at the glass–water interface at an angle i, it emerges finally parallel to the surface of water, then the value of μg would be

#### SOLUTION

Solution :B

For glass water interface gμω=sinisinr.....(i) and For water-air interface ωμa=sinrsin90......(ii)

∴gμωxωμa=sini⇒μg=1sini

### Question 12

A ray of light passes from vacuum into a medium of refractive index μ,the angle of incidence is found to be twice the angle of refraction. Then the angle of incidence is

#### SOLUTION

Solution :B

By using μ=sinisinr⇒μ=sin2rsinr=2sinrcosrsinr

⇒r=cos−1(μ2).So,i=2r=2cos−1(μ2)

### Question 13

On a glass plate a light wave is incident at an angle of 60∘. If the reflected and the refracted waves are mutually perpendicular, the refractive index of material is

#### SOLUTION

Solution :B

from figure

Angle of refraction =∠r

Angle of incidence is equal to angle of reflection [law of reflection]

∴ Angle of reflection =60∘

Given that reflected and refracted ray are perpendicular.

From figure

60∘+90∘+∠r=180∘ [angle sum property]

∠r=30∘

∠i=60∘,∠r=30∘

so μ=sin60sin30=√3

### Question 14

A double convex lens, lens made of a material of refractive index μ1 is placed inside two liquids or refractive indices μ2 and μ3, as shown μ2>μ1>μ3. A wide, parallel beam of light is incident on the lens from the left.

#### SOLUTION

Solution :D

As μ2>μ1, the upper half of the lens will become diverging.

As μ1>μ3, the lower half of the lens will become converging

### Question 15

If ε0 and μ0 are respectively, the electric permittivity and magnetic permeability of free space, ε and μ the corresponding quantities in a medium, the refractive index of the medium is

#### SOLUTION

Solution :B

R.I=C0C=√μ∈μ0∈0=