# 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