# Competitive Exams: Physics MCQs (Practice_Test 16 of 35)

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For measuring potential difference in a circuit a potentiometer is a superior instrument as compared to a voltmeter because it has

greater sensitivity

a low internal resistance at null-point

an infinitely large internal resistance at null-point

zero internal resistance at an currents

An aircraft with a wing span of 20 m flies at a horizontal speed of 360 km/h in a region where the vertical component of the earth's field is 5 × 10 − 5 T. The potential difference between the tips of the wings will be

0.10 V

0.15 V

0.20 V

0.30 V

A current passing through a self-inductance of 2 mH changes at the rate of 20 mA/s. The emf induced in the coil is

10mV

40 mV

10mV

40mV

Two inductors, 0.4 H and 0.6 H are connected in parallel. If this combination is connected in series with an inductor of inductance, 0.76 H, then the equivalent inductance of the circuit will be

2.0 H

1 H

0.2 H

0.1 H

The magnetic field energy in an inductor changes from minimum to maximum value in 2.5 × 10 − 3 s when connected to an ac source. The frequency of the source is

12.5 Hz

25 Hz

50 Hz

100 Hz

The power factor of a series LCR circuit connected to an ac source of frequency, w is given by

Two parallel wires separated by 25 cm carry currents of i1 = 25A and i2 = 35 A flowing in opposite direction. The force per unit length acting between them is

a repulsive force of 7 × 104 N/m

an attractive force of 7 × 10 − 4 N/m

a repulsive force of 35 × 102 N/m

an attractive force of 35 × 102 N/m

In the case of a series LCR circuit, the sharpness of resonance curve is determined by the quality factor ‘Q’ given by

XL/XC

Lw/R at resonance frequency

Lw/R at any frequency other than resonance

Measurement of the Hall emf for a sample gives information about

magnitude and sign of the charge carriers

sign of the charge and density of the carriers

only sign of the charge carriers

only density of the charge carriers

A device used to measure the magnetic field makes use of Hall effect. In a magnetic field of 200 G, it gives a Hall voltage of 16mV: If with the same current and orientation, it gives a Hall voltage of 24 mV in another field, then its magnitude is

1600 G

480 G

300 G

150 G

For a certain thermocouple, the emf = at + bt2 where t (in 0C) is the temperature the hot junction, the cold junction being at 0'C. If = 10 mV/ ‘C and b = 0.02 mV/’ C2 then the temperature (degree C) of inversion, will be

150

250

500

750

In an electromagnetic wave, the direction of the magnetic induction B is:

parallel to the electric field %

perpendicular to the electric field %

anti parallel to the Pointing's vector, S

Random

If an electromagnetic wave is propagating in a medium with permittivity and permeability m, then m/is the

intrinsic impedance of the medium

square of the refractive index of the medium

refractive index of the medium

energy density of the medium

A cyclotron magnet has pole pieces of radius R and produces a maximum magnetic field B. The maximum energy to which charged particle can be accelerated is proportional to

BR

B2R2

B2R

BR2