Physic Tutorials

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


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


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


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


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



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

Read short note on magnetic field and em induction

Bolarinwa Olajire

An associate lecturer at MAPOLY with demonstrated history of working in the education industry. Skilled in analytical skills, C++, Fortran, and Entrepreneurship. Strong education professional with a M. SC focused in condensed matter from University of Ibadan and PhD student at FUNAAB.

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