# Magnetism

**Section 1.**

Q1. Give some properties of magnets.

Q2. Explain the difference between magnetic north and true north.

Q3. Give some applications of the earth’s magnetic field.

Q4. What happens to an electron when it enters a magnetic field?

Q5. An electron enters a magnetic field of magnetic flux density 8T at right angles to the field. It is moving at a speed of 750m/s, find the radius of the path it follows.

**Section 2.**

Q1. How would you plot the electric field around a current carrying conductor.

Q2. Explain the right hand grip rule.

Q3. What is the difference between a coil and a solenoid?

Q4. Draw two diagrams, one which shows the field around a coil and the other which shows the field around a solenoid.

Q5. Name the materials which are attracted by magnets. What is a natural magnet made of?

**Section 3.**

1. Describe (with the aid of a diagram) how to demonstrate that a current-carrying conductor in a magnetic field experiences a force.

Indicate clearly the direction of the force by putting in directions for current and magnetic field.

2. List three items which operate on this principle.

3. Calculate the force acting on a conductor of length 40 cm which is carrying a current of 3 A and which is placed perpendicular to a uniform magnetic field of flux density 5.2 T.

4. A particle of charge 2 x 10^{-3} C moving at 100 ms^{-1} moves at right angles to a uniform magnetic field of flux density 3 T. What is the force on the charge?

5. Define the Ampere.

**Electromagnetic Induction**

**Section 4.**

Q1. What is electromagnetic induction?

Q2. Describe an experiment to demonstrate electromagnetic induction.

Q3. State Faraday’s law of electromagnetic induction.

Q4. Describe an experiment which demonstrates Faraday’s law.

**Section 5.**

Q1.State Lenz’s law of electromagnetic induction.

Q2. Describe an experiment which demonstrates Lenz’s law.

Q3. Define magnetic flux .

Q4. A coil has 5000 turns. What is the emf induced in the coil when the magnetic flux cutting the coil changes by 8 × 10^{–4} Wb in 0.1 s?

Q5. A 100 turn coil of area .08 m squared is placed in a uniform magnetic field of flux density 2 T. If the flux density increases to 6 T in 0.5 s, find the average induced emf in the coil.

**Section 6.**

Q1. State the three laws of electromagnetic induction.

Q2. What is the term used to describe the strength of a magnet? What are the units of this quantity?

Q3. Define magnetic flux?

Q4. What is a capacitor?

Q5. What is the difference between AC & DC?

**Section 7.**

Q1. What device would you use to convert AC to DC?

Q2. If a current carrying conductor has a current of 2 amps flowing in it and is 78cm long what is the force it feels if the magnetic flux density is 7.5 Tesla?

Q3. How would you demonstrate Faraday’s law in the lab?

Q4. What is magnetic flux? Give the formula for it. What unit is it measured in?

Q5. If a magnet has a magnetic flux density of 10 T what is the magnetic flux if the area of the loop is 0.5 square meters?

**Section 8.**

Q1. Find the magnetic flux of a square loop of side 10cm in a magnetic field of flux density 3T.

Q2. Find the magnetic flux of a circular loop of radius 5cm in a magnetic flux density of 2.5T.

Q3. Find the magnetic flux of a circular loop which is at an angle of 35 degrees to the perpendicular of a magnetic field of flux density of 4.2T.

Q4. If the magnetic flux density is 10 Wb on a loop in a magnetic field to 5T find the area of the loop.

Q5. Find the length of the side of the loop in Q4 if it was a square loop. Find the diameter of of the loop in Q4if it was a circular loop.

**Sdection 9.**

Q1. A square coil of side 5 cm lies perpendicular to a magnetic field of flux density 4.0 T.

The coil consists of 200 turns of wire.

(i) What is the magnetic flux cutting the coil?

(ii) The coil is rotated through an angle of 90o in 0.2 seconds. Calculate the magnitude of the average

e.m.f. induced in the coil while it is being rotated.

Q2. A light aluminium ring is suspended from a long thread.

When a strong magnet is moved away from it, the ring follows the magnet.

(i) Explain why.

(ii) What would happen if the magnet were moved towards the ring?