Light Reflection and Refraction Test

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Light Reflection and Refraction Test - 66

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Weekly Quiz Competition

Question 1
1 / -0

From the base of a hollow cone of height $$ h $$ with a small angle at the top, a small ring was cut off and placed in front of a parallel beam of light (the figure is exaggerated for clarity). At what distance x will rays of light reflected from it intersect the axis of the cone.

A
$$ h $$

B
$$ \dfrac{h}{2} $$

C
$$ \dfrac{h}{\sqrt{2}} $$

D
$$ \sqrt{\dfrac{2}{3}} h $$
Question 2
1 / -0

Select the correct alternative (s) :

A
A convex lens may form a real image

B
$$R=2f$$ formula is applicable to only paraxial ray

C
A convex lens becomes less convergent when it is immersed in water

D
All of the above

Solution
Question 3
1 / -0

You are provided with a convex mirror, a concave mirror, a convex lens and a concave lens. You can get an inverted image from

A
Both concave lens and convex lens.

B
Both concave mirror and convex mirror.

C
Both concave mirror and convex lens.

D
Both convex mirror and concave lens.

Solution

concave mirror forms - inverted image
Convex mirror forms - erect image
Concave lens forms - erect image
Convex lens forms - inverted image
Question 4
1 / -0

A ray of light moving from an optically rarer to a denser medium

A
Bends away from the normal

B
Bends towards the normal

C
Remains undeviated

D
None of the above

Solution

A ray of light moving from an optically rarer to a denser medium then bends towards the normal. While when a ray of light moves from denser to rarer then it bends away from the normal.
Question 5
1 / -0

When a ray of light from air enters a denser medium, it:

A
bends away from the normal

B
bends towards the normal

C
goes undeviated

D
is reflected back

Solution

The ray of light bends towards the normal.
$$\text{Reason:}$$ As the speed of light decreases in the denser medium, it bends towards the normal.
Question 6
1 / -0

The refractive indices of glass and water w.r.t air are $$\dfrac{3}{2}$$ and $$\dfrac{4}{3}$$ respectively. The refractive index of glass w.r.t water will be

A
$$\dfrac{8}{9}$$

B
$$\dfrac{9}{8}$$

C
$$\dfrac{7}{6}$$

D
None of these

Solution

As we know,
$$_a\mu_{g}=\dfrac {3}{2}, _a\mu_{w}=\dfrac {4}{3}$$
$$\therefore \ _w\mu_{g}=\dfrac {_a\mu_{g}}{_a\mu_{w}}=\dfrac {3/2}{4/3}=\dfrac 98$$
Question 7
1 / -0

If aperture of lens is halved then image will be

A
No effect on size

B
Intensity of image decreases

C
Both $$(a)$$ and $$(b)$$

D
None of these

Solution

Since , aperture only effects the number of rays passing through the lens.
Hence, intensity of image $$\propto$$ (Aperture).

Therefore, intensity of image will decrease if aperture of lens is halved but there will be no change in the size.
Question 8
1 / -0

Absolute refractive indices of glass and water are $$\dfrac {3}{2}$$ and $$\dfrac {4}{3}$$. The ratio of velocity of light in glass and water will be

A
$$4:3$$

B
$$8:7$$

C
$$8:9$$

D
$$3:4$$

Solution

We know that , $$\mu = \dfrac{c}{v} \Rightarrow v=\dfrac{c}{\mu}$$

Since, $$c$$ is constant, we can say that

$$v\propto \dfrac {1}{\mu}\Rightarrow \dfrac {v_1}{v_2}=\dfrac {\mu_2}{\mu_1}$$

Given that, $$\mu_g = \dfrac{3}{2}$$ and $$\mu_w = \dfrac{4}{3}$$

$$\Rightarrow \dfrac {v_g}{v_w}=\dfrac {\mu_w}{\mu_g}=\dfrac {4/3}{3/2}=\dfrac {8}{9}$$
Question 9
1 / -0

The refractive index of water with respect to air is $$4/3$$ and the refractive index of glass with respect to air $$3/2$$. The refractive index of water with respect to glass is

A
$$\dfrac 98$$

B
$$\dfrac 89$$

C
$$\dfrac 12$$

D
$$2$$

Solution

As we know,
$$_g\mu_w =\dfrac {\mu_w}{\mu_g}=\dfrac {4/3}{3/2}=\dfrac {8}{9}$$
Question 10
1 / -0

Which of the following is a correct relation?

A
$$_a \mu_r = _a\mu_w \times _r \mu_w$$

B
$$_a \mu_r \times _r \mu_w = _r \mu_a$$

C
$$_a \mu_r \times _r \mu_a =0$$

D
$$\dfrac{_a \mu_r}{_w \mu_r} = _a \mu_w$$

Solution

As we know,
Refractive index of medium 2 w.r.t. medium 1
$$_1\mu_2=\dfrac{speed \ of \ light \ in \ medium \ 1}{speed \ of \ light \ in \ medium \ 2}=\dfrac{v_1}{v_2}$$

If we divide numberator and denominator by $$c$$, then we get
$$_1\mu_2=\dfrac{v_1/c}{v_2/c}=\dfrac{v_1}{c} \times \dfrac{c}{v_2} = \dfrac{\mu_2}{\mu_1}$$

This is how we write relative refractive index of medium 2 w.r.t medium 1 in terms of absolute refractive indices of 1 and 2. So let us simplify and check which option is correct.

Option A:
LHS: $$_a\mu_r=\dfrac{\mu_r}{\mu_a}$$
RHS: $$_a\mu_w \times _r\mu_w= \dfrac{\mu_w}{\mu_a} \times \dfrac{\mu_w}{\mu_r}$$
LHS and RHS are not equal.

Similarly Option B is also incorrect.

Option C:
It is clearly wrong as product of two non-zero numbers can't be zero.

Option D:
$$\dfrac {_a\mu_r}{_w\mu_r}=\dfrac {\mu_r /\mu_a }{\mu_r / \mu_w }=\dfrac {\mu_w }{\mu_a }= _a\mu_w$$

So option D is correct.

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Re-Attempt Weekly Quiz Competition

Light Reflection and Refraction Test - 66

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Light Reflection and Refraction Test - 66

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Question 1

$$ h $$

$$ \dfrac{h}{2} $$

$$ \dfrac{h}{\sqrt{2}} $$

$$ \sqrt{\dfrac{2}{3}} h $$

Question 2

A convex lens may form a real image

$$R=2f$$ formula is applicable to only paraxial ray

A convex lens becomes less convergent when it is immersed in water

All of the above

Solution

Question 3

Both concave lens and convex lens.

Both concave mirror and convex mirror.

Both concave mirror and convex lens.

Both convex mirror and concave lens.

Solution

Question 4

Bends away from the normal

Bends towards the normal

Remains undeviated

None of the above

Solution

Question 5

bends away from the normal

bends towards the normal

goes undeviated

is reflected back

Solution

Question 6

$$\dfrac{8}{9}$$

$$\dfrac{9}{8}$$

$$\dfrac{7}{6}$$

None of these

Solution

Question 7

No effect on size

Intensity of image decreases

Both $$(a)$$ and $$(b)$$

None of these

Solution

Question 8

$$4:3$$

$$8:7$$

$$8:9$$

$$3:4$$

Solution

Question 9

$$\dfrac 98$$

$$\dfrac 89$$

$$\dfrac 12$$

$$2$$

Solution

Question 10

$$_a \mu_r = _a\mu_w \times _r \mu_w$$

$$_a \mu_r \times _r \mu_w = _r \mu_a$$

$$_a \mu_r \times _r \mu_a =0$$

$$\dfrac{_a \mu_r}{_w \mu_r} = _a \mu_w$$

Solution

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