Practice Pakistan's most useful MCQs for competitive exams

An aeroplane of wingspan 10m flies from the equator towards the North Pole. The wings are perpendicular to the vertical component of the earths magnetic field (B = 4×10-5T). At maximum speed an emf of 96mV is induced across the wing tips. The maximum speed of the aeroplane is____________?

• (A)  150msec-1
• (B)  384msec-1
• (C)  38.4msec-1
• (D)  200msec-1

Answer

Submitted By :Ali Uppal

Non inductive resistances are used in decreasing______________?

• (A)  Mutual inductance
• (B)  Self inductance
• (C)  Magnetic fields
• (D)  Heating effect

Answer

Submitted By :Ali Uppal

Which one of the following devices does not function like an electric motor ?

• (A)  Galvanometer
• (B)  Ammeter
• (C)  Voltmeter
• (D)  Transformer

Answer

Submitted By :Ali Uppal

For long distance transmission the transformer used is_____________?

• (A)  Step down
• (B)  Input voltage and output voltage remain same
• (C)  Step up
• (D)  Amplifier is used

Answer

Submitted By :Ali Uppal

Lagging of changes in the magnetization of a substance behind changes in the magnetic field as the magnetic field is varied is known as magnetic_____________?

• (A)  Retaintivity
• (B)  Permeability
• (C)  Flux
• (D)  Hysteresis

Answer

Submitted By :Ali Uppal

When the motor is at its maximum speed then back emf will be______________?

• (A)  Maximum
• (B)  Zero
• (C)  Intermediate values
• (D)  No back emf

Answer

Submitted By :Ali Uppal

Transformer works on the principle of________________?

• (A)  Lenzs law
• (B)  Faradays law
• (C)  Mutual induction
• (D)  Law of conservation of power

Answer

Submitted By :Ali Uppal

Electric force between two point charges in air or vacuum is F. If we replace air or vacuum by an insulator (dielectric) of relative permitivity Cr the force between the charges will_______________?

• (A)  decrease
• (B)  increase
• (C)  remain constant
• (D)  depends upon composition of dielectric

Answer

Submitted By :Ali Uppal

The minimum charge on any object cannot be less than_______________?

• (A)  1.6 x 10-19C
• (B)  3.2 x 10-19C
• (C)  9.1 x 109C
• (D)  no definite value exist

Answer

Submitted By :Ali Uppal

When we rub a glass rod with a silk cloth then________________?

• (A)  glass rod acquires negative charge while silk acquires positive charge
• (B)  glass rod acquires positive charge while silk acquires negative charges
• (C)  both glass rod and silk acquire negative charge
• (D)  both glass rod and silk acquire positive charge

Answer

Submitted By :Ali Uppal