A concave mirror is placed over a beaker containing water of (µ = 1.33) and image of the object placed at the bottom of beaker is formed at a distance of 25 cm from the top then focal length of the mirror is

A glass of refractive index 1.5 is coated with a thin layer of thickness of tt of refractive index 1.8 light of wavelength λ tavelling at the upper and the lower surfaes of the layer and the two reflected rays interfere. If λ=648nm , obtain the least value of tt (in 10⁻⁸m) for which the rays interfere constructively.

1) 1.8 ×10⁻⁸m

2) 0.9 ×10⁻⁸m

3) 9×10⁻⁸m

4) 18×10⁻⁸m

A diode can convert
1. ac to dc
2. dc to ac
3.ac to dc and vice versa
4.None of the above

If the value of gravitational acceleration at a height h above the Earth's surface is the same as that at a depth d below the Earth's surface (with both h and d small compared to the Earth's radius R), then
 
 1) h = 2 d
 2) h = d
 3) h = d2 / R
 4) h = d / 2

 A cart of mass has a block of mass m attached to it as shown in figure. The coefficient of friction between the block and the cart is µ. What is the minimum acceleration of the cart so that the block m does not fall

1)µg
2) g/µ
3)µ/g
4)Mµg/m

A wave of frequency 400 Hz has a velocity 360 m/s. The distance between two nearest points which are 60° out of phase, is:
1.12 cm
2. 14 cm
3.10 cm
4.15 cm

A composite string is made by joining two strings of different masses per unit length μ and 4μ. The composite string is under the same tension. A transverse wave pulse Y = (6 mm) sin (5t + 40x), where t is in seconds and x is in meters, is sent along the lighter string towards the joint. The joint is at x = 0. The equation of the wave pulse reflected from the joint is

1) Y = (2 mm) sin (5t – 10x)
2) Y = (4 mm) sin (40x – 5t)
3) Y = –(2 mm) sin (5t – 40x)
4) Y = (2 mm) sin (5 t – 40x)

A car travels 90. meters due north in 15 seconds. Then the car turns around and travels 40. meters due south in 5.0 seconds. What is the magnitude of the average velocity of the car during this 20.-second interval?
 
 1) 2.5 m/s
 2) 5.0 m/s
 3) 6.5 m/s
 4) 7.0 m/s

Equal potentials are applied on an iron and a copper wire of same length. In order to have the same current flow in the two wires, the ratio r(iron) / r(copper) of their radii must be: [specific resistance of iron = 1.0 ]

1) 2.4 : 1
2) 1 : 2.4
3) 1.2 : 1
4) 1 : 1.2

 The max. value of magnetic field in a electric field 3.2 x 10^-4 v/m (max. value) :

(1) 0.94 x 10^-14 T 
(2) 0.94 x 10¹⁰ T
(3) 1.07 x 10^-12 T
(4) 1.07x10^-9T