Questions and answers on Magnetic field and E.M induction for UTME
Question 1
Induced emfs are best explained using{UTME 2013}
A. Lenz’s law B. Ohm’s law C. Faraday’s law D. Coulomb’s law
Solution
Athough both Faraday and Lenz explained the induced emf
Faraday’s law talk about the emf is induced as a result of the rate of change of magnetic flux linkage while
Lenz says the the induced emf move in such a way as to oppose the change producing
Look at the two theory Faraday BEST explained induced emf
C is the correct option
Question 2
A conductor of length 1m moves with a velocity of 50ms-1 at an angle of 300 to the direction of a uniform magnetic
field of flux density 1.5 Wbm-2. What is the e.m.f. induced in the conductor?{UTME 2012}
A. 37.5V B. 50.5V C. 75.0V D. 80.5V
Solution
E = Blv sinQ
E = 1.5 * 1 * 50 sin30
E = 37.5 v
A is the correct answer
Question 3
A particle carrying a charge of 1.0 x10-8C enters a magnetic field at 3.0 x102 ms-1 at right angles to the field. If
the force on this particle is 1.8 x 10-8N, what is the magnitude of the field?{UTME 2012}
A. 6.0 x 10-1T B. 6.0 x 10-2T C. 6.0 x 10-3T D. 6.0 x 10-4T
Solution
F = Bqv
B = F / qv
B = 1.8 x 10-8 / (1.0 x10-8 * 3 x 102)
B = 0.6 x 10-2 = 6.0 x 10-3 T
C is the correct option
Question 4
A step-down transformer has a power output of 50W and efficiency of 80%. If the mains supply voltage is 200V,
calculate of the primary current of the transformer.{UTME 2008}
A. 0.31A B. 3.20A C. 3.40A D. 5.00A
Solution
efficiency = power output / power input
80/100 = 50/power input
50*100 / 80 = power input
power input = 62.5
power input = IpVp
Ip = 62.5 / 200 = 0.31 A
A is the correct option
Question 5
Two long parallel wires X and Y carry currents 3A and 5A respectively. If the force experienced per unit length by X is 5 x 10-5N, the force per unit length experienced by wire Y is{UTME 2007}
A. 3 x 10-5N B. 3 x 10-6N C. 5 x 10-4N D. 5 x 10-5N
Solution
Following the above formula and supporting it with Newton’s third law that states the if object X exert a force on object y, object y will exert the same force on X but in opposite direction.
For two parallel current carrying conductor, regardles of their current, they will exert the same force on each other but in opposite direction
D is the correct answer
