The magnetic moment of a magnet is 0.1 amp × m². It is suspended in a magnetic field of intensity 3 × 10^-4weber/m².The couple acting upon it when deflected by 30º from the magnetic field is

1 × 10^–5N m
1.5 × 10^–5N m
2 × 10^–5N m
2.5 × 10^–5N m

Solution

τ= MB sin θ= 0.1 × 3 × 10^–4 sin 30º

or τ = 1.5 × 10^–5N–m

In the displacement method, a concave lens is placed in between an object and a screen. If the magnification in the two positions are m₂and m₂(m₁ > m₂), and the distance between the two positions of the lens is x, the focal length of the lens is

\(\frac{x}{m_{1}+m_{2}}\)
\(\frac{x}{m_{1}-m_{2}}\)
\(\frac{x}{(m_{1}+m_{2})^{2}}\)
\(\frac{x}{(m_{1}-m_{2})^{2}}\)

Which of the following has/have zero average value in a plane electromagnetic wave ?

Both magnetic and electric field
Electric field only
Magnetic energy
Electric energy

Solution

Both magnetic and electric fields have zero average value in a plane e.m. wave.

DIRECTIONS: Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following-

Statement 1 : Shortwave bands are used for transmission of radio waves to a large distance.

Statement 2 :Short waves re reflected by ionosphere

(a)Statement -1 is false, Statement-2 is true
(b)Statement -1 is true, Statement-2 is true; Statement -2 is a correct explanation for Statement-1
(c)Statement -1 is true, Statement-2 is true; Statement-2 is not a correct explanation for Statement-1
(d)Statement -1 is true, Statement-2 is false

Solution

(c)Statement -1 is true, Statement-2 is true; Statement-2 is not a correct explanation for Statement-1

Short wave (wavelength 30 km to 30 cm). These waves are used for radio transmission and for general communication purpose to a longer distance from ionosphere.

If the molecules of a gas have f degrees of freedom, the ratio C_p/C_v of the gas is equal to :

1+^f⁄₂
1+²⁄_f
¹⁄₂+f
^1+f⁄₂

Solution

^C_p⁄_{C_v} = 1 + ²⁄_f

N molecules, each of mass m,of gas A and 2 N molecules,each of mass 2 m, of gas B are contained in the same vessel which is maintained at a temperature T. The mean square of the velocity of molecules of B type is denoted by v² and the mean square of the X component of the velocity of A type is dentoed by ω², ω²/v² is

Solution

DIRECTIONS: Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following-

Statement 1 : Radio waves can be polarised.

Statement 2 :Sound waves in air are longitudinal in nature.

(a)Statement -1 is false, Statement-2 is true
(b)Statement -1 is true, Statement-2 is true; Statement -2 is a correct explanation for Statement-1
(c)Statement -1 is true, Statement-2 is true; Statement-2 is not a correct explanation for Statement-1
(d)Statement -1 is true, Statement-2 is false

Solution

(c)Statement -1 is true, Statement-2 is true; Statement-2 is not a correct explanation for Statement-1

Radio waves can be polarised because they are transverse in nature. Sound waves in air are longitudinal in nature.

The efficiency of carnot engine when source temperature is T₁ and sink temperature is T₂ will be

\(\frac{T_{1}-T_{2}}{T_{1}}\)
\(\frac{T_{1}-T_{2}}{T_{1}}\)
\(\frac{T_{1}-T_{2}}{T_{2}}\)
\(\frac{T_{1}-T_{2}}{T_{2}}\)

Solution

Efficiency of carnot engine\(\eta =\frac{T_{1}-T_{2}}{T_{1}}\)

where T₁ =source temperature
T₂ =sink temperature.

DIRECTIONS : Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following-

(a)Statement -1 is false, Statement-2 is true

(b)Statement -1 is true, Statement-2 is true; Statement -2 is a correct explanation for Statement-1

(c)Statement -1 is true, Statement-2 is true; Statement -2 is not a correct explanation for Statement-1

(d)Statement -1 is true, Statement-2 is false

Statement-1 : For a charged particle moving from point P to point Q, the net work done by an electrostatic field on the particle is independent of the path connecting point P to point Q.

Statement-2 :The net work done by a conservative force on an object moving along a closed loop is zero.

View Ans & Explanation
(b)Statement -1 is true, Statement-2 is true; Statement -2 is a correct explanation for Statement-1

Statement 1 is true. Statement 2 is true and is the correct explanation of statement 1.

A uniform wire of length 20 m and weighing 5 kg hangs vertically.If g = 10 m/s², then the speed of transverse waves in the middle of the wire is

10 m/s
10²m/s
4 m/s
zero

Solution

When heat is given to a gas in an isothermal change, the result will be

external work done
rise in temperature
increase in internal energy
external work done and also rise in temperature

Which of the following is not due to total internal reflection?

Working of optical fibre
Difference between apparent and real depth of pond
Mirage on hot summer days
Brilliance of diamond

Solution

Difference between apparent and real depth of a pond is due to the refraction of light, not due to the total internal reflection. Other three phenomena are due to the total internal reflection.

The net magnetic moment of two identical magnets each of magnetic moment M₀, inclined at 60° with each other is