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nAmIB I A U n IVERS ITY OF SCIEnCE AnD TECHnOLOGY

FACULTY OF HEALTH AND APPLIED SCIENCES

DEPARTMENT OF NATURAL AND APPLIED SCIENCES

QUALIFICATION: BACHELOR OF SCIENCE

QUALIFICATION CODE: 07BOSC LEVEL: 6

COURSE CODE: EAM601S COURSE NAME: ELECTRICITY AND MAGNETISM

SESSION: JULY 2016 PAPER: THEORY

DURATION: 3 HOURS MARKS: 100

SECOND OPPORTUNITY EXAMINATION QUESTION PAPER

EXAMINER(S) Dr. Dipti Ranjan Sahu

MODERATOR: Dr. AI-Mas Sendegeya

INSTRUCTIONS 1. Answer ALL the questions.

2. Write clearly and neatly.

3. Number the answers clearly.

PERMISSIBLE MATERIALS

Non-programmable Calculators

THIS QUESTION PAPER CONSISTS OF 4 PAGES {Includ ing this front page)

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Section A: Multiple-choice questions

Question 1 Each question carries 2 marks

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

At what separation will two charges, each of magnitude 6.0 J.!C, exert a force of 1.4 Non each other?

A. 5.1 x 10-6 m B. 0.23m C. 0.48m D.2.0m

Two wires are ofthe same length, same radius, but one ofthem is of copper and the other is of iron. Which will have more resistance?

A. Copper B. Iron C. Both have same resistance D. None of these

How much work is done in moving a charge of 3 coulumb from a point at the volts 115 to a point at 125 volts? A. 20 Joules B. 30 Joules C. 420 Joules D. 375 Joules

Electric current originates from which part of an atom A. nucleus B. entire atom acting as a unit C. positively charged protons D. negatively charged electrons

Voltage is a form of A. Kinetic energy B. Potential energy C. both Potential and Kinetic energy D. None of the above.

Which of the following is not an electrical classification of materials A. Semiconductors B. Semi-insulators C. insulators D. Conductors

If the cross-sectional area of a magnetic field increases, but the flux remains the same, the flux density A. decreases B. doubles C. Increases D. remains the same

An electromagnetic field exists only when there is A. Voltage B. an increasing current C. current D. decreasing current

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1.9 What is the magnetomotive force (mmf) of a wire with 8 turns carrying three amperes of current? A. 240 At B. 24 At C. 2.4 At D. 2400 At

1.10 When the speed at which a conductor is moved through a magnetic field is increased, the induced voltage A. increases B. decreases C. remains constant D. reaches zero

Section B Question 2

2.1

2.2

2.3

2.4.

2.5.

2.6

What is Ohm's Law? Do all conductor obey Ohm"s Law?

What is the differnec between resitance and resistivity?

What is Lenz' s law and how can you find polarity of induced emf if no current flows, using Lenz's law

What is fuse? How is the fuse connected in an electric circuit? Why fuses are usually made of tin alloy?

What is electric potential energy? Derive the expression for the potential energy of a continuous charge distribution (conducting Sphere).

What is electric flux? Find the electric flux through a sphere of radius 1.0 m containing a charge of+ 1 f.lC at its centre.

Section C

3. A 36-m length wire carries a current of22A running from right to left. Calculate the magnitude and direction of the magnetic force acting on the wire

if it is placed in a magnetic field with a magnitude of 0.50 x 1 o-4 T and directed up the page.

MAGNETIC FIELD

ｾｾ＠ ｊｾ＠ ｊｾ＠ J, ｾｾ＠ Ｎ ｊｾ＠

4. A parallel-plate capacitor has plates of dimensions 2.0 em by 3.0 em separated by a 1.0 mm thickness of paper. The Dielectric constant of paper is 3. 7.

The dielectric strength of paper is 16 x 106 V /m.

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5.

6.

(i)

(ii)

(iii)

(a)

(b)

Find its capacitance.

The maximum voltage that can be applied before breakdown

What is the maximum charge that can be placed on the capacitor? Use, Eo= 8, 85 X I o-'2 C2.N-' .m-2.

What is Ampere's law?

Differentiate between Gauss's and Ampere's laws.

Calculate the charge on the 30 mF capacitor in the circuit below and also the voltage across each capacitor.

20tnF 30 mF

30V ?Q 1nF

7. For the circuit below calculate (a) current through the circuit (b) Potential difference between point a and b (c) Potential difference between point band c (d) Potential difference between point a and c

6V b a

20 10

30

6V c

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