PROBLEM FORMULA TEST VOL II

An object is placed at a distance of 20.0 cm from a concave mirror of focal length 15.0 cm. (a) What distance from the mirror a screen should be placed to get a sharp image? (b) What is the nature of the image?

• $\frac{1}{v}\ +\frac{1}{u}\ =\ \frac{1}{f}\ \$

• $\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$

• $\frac{1}{v}+\frac{1}{u}=\frac{1}{R}$

• $\frac{1}{R}+\frac{1}{u}=\frac{1}{f}$

A thin rod of length f /3 is placed along the optical axis of a concave mirror of focal length f such that one end of image which is real and elongated just touches the respective end of the rod. Calculate the longitudinal magnification.

• $m_1=\frac{lengthofimage}{lengthofobject}$

• $m_1=\frac{lengthoflense}{lengthofobject}$

• $m_1=\frac{lengthofimage}{lengthoflense}$

• $m_1=\frac{lengthof\ object}{lengthofimage}$

Pure water has refractive index 1.33. What

is the speed of light through it?

• $n=\frac{c}{v}$

• $n=\frac{c}{n_2}$

• $n=\frac{v}{c}$

• $n=\frac{n_2}{c}$

Light travelling through transparent oil enters in to glass of refractive index 1.5. If the refractive index of glass with respect to the oil is 1.25, what is the refractive index of the oil?

• $n_{og}=\frac{n_g}{n_o}$

• $n_{go}=\frac{n_g}{n_o}$

• $n_{og}=\frac{n_o}{n_g}$

• $n_{go}=\frac{n_o}{n_g}$

A optical fibre is made up of a core

material with refractive index 1.68 and

a cladding material of refractive index

1.44. What is the acceptance angle of the

fibre if it is kept in air medium without

any cladding?

• $i_a=\sin^{-1}\sqrt{n_1^2-n_2^2}$

• $i_a=\sin\left(\sqrt{n_1^2-n_2^2}\right)$

• $i_a=\sin^{-1}\sqrt{n_2^2-n_1^2}$

• $i_a=\sin\left(\sqrt{n_2^2-n_1^2}\right)$

The thickness of a glass slab is 0.25 m.

It has a refractive index of 1.5. A ray of light

is incident on the surface of the slab at an

angle of 60o. Find the lateral displacement

of the light when it emerges from the other

side of the glass slab.

• $\sin i=\frac{\sin r}{n}$

• $\sin i=\frac{n}{\sin\ r}$

• $\sin r=\frac{\sin i}{n}$

• $\sin r=\frac{n}{\sin i}$

Locate the image of the point object O in the situation shown. The point C denotes the centre of curvature of the separating surface.

• $\frac{n_2}{v}-\frac{n_1}{u}=\frac{n_2-n_1}{R}$

• $\frac{n_2}{u}-\frac{n_1}{v}=\frac{n_2-n_1}{R}$

• $\frac{n_1}{v}-\frac{n_2}{u}=\frac{n_2-n_1}{R}$

• $\frac{n_2}{v}-\frac{n_1}{u}=\frac{n_1-n_2}{R}$

A biconvex lens has radii of curvature 20 cm

and 15 cm for the two curved sufaces. The

refractive index of the material of the lens

is 1.5.

(a) What is its focal length?

(b) Will the focal length change if the lens

is flipped by the side?

• $\frac{1}{R}=\left(n-1\right)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)$

• $\frac{1}{R}=\left(n-1\right)\left(\frac{1}{R_2}-\frac{1}{R_1}\right)$

• $\frac{1}{f}=\left(n-1\right)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)$

• $\frac{1}{f}=\left(n-1\right)\left(\frac{1}{R_2}-\frac{1}{R_1}\right)$

The wavelength of light from sodium source in vacuum is 5893Å.What are its (a) wavelength, (b) speed and (c) frequency when this light travels in water which has a

refractive index of 1.33.

• $\frac{\lambda_1}{\lambda_2}=\frac{n_1}{n_2}$

• $\frac{\lambda_2}{\lambda_1}=\frac{n_1}{n_2}$

• $\frac{\lambda_1}{\lambda_2}=\frac{n_2}{n_1}$

• $\frac{\lambda_2}{\lambda_1}=\frac{n_2}{n_1}$

Two light sources with amplitudes 5 units

and 3 units respectively interfere with each

other. Calculate the ratio of maximum and

minimum intensities.

• $A=\sqrt{a_1^2+a_2^2+2a_1a_2\cos\phi}$

• $A=\sqrt{a_1^2+a_2^2-2a_1a_2\cos\phi}$

• $A=\sqrt{a_1^2+a_2^2+2a_1a_2\sin\phi}$

• $A=\sqrt{a_1^2+a_2^2-2a_1a_2\sin\phi}$