Physics Past Questions and Answers

Lenz's law of electromagnet states that

A The induced charge is constant for a fixed change of force
B A force is exerted on a current-carrying conductor in a magnetic field
C The magnitude of the induced e.m.f in a circuit is proportional to the rate of change of the number of lines of force linking the circuit
D The induced current in a conductor is in such a direction as to oppose the change producing it
E E.m.f. is induced in a circuit whenever there is a change in the magnetic flux linked with the circuit

Question 632:

A proton of charge 1.6 x 10¹⁹C is projected into a uniform magnetic field of flux density with a constant speed of 1.6 x 10⁶ms^-1, calculate the magnitude of the force exerted on it by the field

A 0.0N
B 2.0 x 10^-21N
C 1.3 x 10^-17N
D 5.1 x 10^-14N
E 2.3 x 10¹³N

Question 633:

The direction of the magnetic field at a point in the vicinity of a bar magnetic is

A Along the line joining the point to the neutral point
B Always away from the south pole of the magnet
C Opposite the direction of theresultant field at that point
D Always towards the north pole of the magnet
E The direction towards which the north pole of a compass needle would point

Question 634:

The diagram below illustrates an a.c.source of 50V(r.m.s.), \(\frac{100}{\pi}\)Hz connected in series with an inductor of inductor of inductance L and a resistor of resistance R. The current in the circuit is 2A and the p.d across L and R are 30V and 40V respectively. Calculate the power factor of the circuit

A 1.33
B 1.25
C 0.80
D 0.75
E 0.60

Question 635:

The diagram below illustrates an a.c.source of 50V(r.m.s.), \(\frac{100}{\pi}\)Hz connected in series with an inductor of inductor of inductance L and a resistor of resistance R. The current in the circuit is 2A and the p.d across L and R are 30V and 40V respectively. Calculate the average power dissipated in the circuit

A 100W
B 80W
C 60W
D 20W
E 10W