Electromagnetismp. 254

Hold current carrying conductor in

right hand.

Thumb points in direction of current.

Fingers indicate direction of magnetic field.

X

Right hand rule

Magnetic field around a wire loop

X

Correct diagram on page 255

Right hand solenoid rule

Hold solenoid in the right hand.

Thumb indicates direction

of magnetic field (North).

Curled fingers indicate

direction of conventional

current.

Homework

Exercise 1

p. 260

nos. 2.6, 4

2.6 Draw sketches to indicate the magnetic field around a straight current carrying conductor when the

current flows …

2.6.1 through the conductor "into" the page, away from you.

2.6.2 through the conductor “out of" the page, towards you.

X

4.1 Indicate the deviation of the compass needles on Fig. 2.

4.2 Draw a sketch of the magnetic field pattern for this circular conductor (loop). On your sketch, indicate the

regions where the magnetic field is the strongest, as well as the magnetic poles.

Faraday’s lawp. 264

Magnetic field (B) measured in Tesla (T), indicated

by field lines crossing through an area (A)

Magnetic field lines

ɸ = BɹA

1 Wb = 1 T.m2

Magnetic flux

ɸ = BAcosθ

Magnetic flux

θ

A square wire loop with a surface of 1,2 m² crosses through a magnetic field of 0,4 T in different

directions, as shown below. Calculate the magnetic field in each case.

Electricity is generated when a solenoid

and a magnet move relative to each other.

Electromagnetic

inductionp. 264

The magnitude of the

induced emf across the

ends of a conductor is

directly proportional to the

rate of change of the

magnetic flux linkage with

the conductor.

Faraday’s law

I.e. the more field

lines crossed by the

turns of the solenoid

per second, the

stronger the current!

Lenz’s Law:

The direction of the induced current is such

that it will oppose that which causes it.

N

N S

N

S N

• The faster the magnet moves, the stronger

the current.

• The more turns, the stronger the current.

The direction of the current changes if the magnet

moves in the opposite direction.

• The stronger the magnet, the stronger the

current.

Ɛ = -NΔɸ

Δ𝑡

Induced EMF

EMF (V)

Number of turns

Lenz’s law Change in

magnetic flux

Homework

Exercise 2

p. 272,

nos. 4, 5, 6, 7, 8, 13

p. 280,

nos. 2.1, 2.4, 3.1, 6

4

5. A solenoid with 450 turns has a cross section surface of 176 cm². It is placed perpendicular in

a uniform magnetic field of 0,72 T.

5.1 Calculate the flux through the solenoid.

5. A solenoid with 450 turns has a cross section surface of 176 cm². It is placed perpendicular in

a uniform magnetic field of 0,72 T.

5.2 Calculate the induced emf if the solenoid is pulled out of the magnetic field in 0,22 s.

6. A solenoid with 500 turns is rotated such that the magnetic flux linked to each turn changes from

6 x 10¯⁴ Wb to 2 x 10¯⁴ Wb in 1,5 s. Calculate the average emf across the ends of the solenoid.

7. A square wire coil with each side 180 mm, contains 200 turns. The magnetic field through the

centre of the coil changes from 0 T to 0,8 T in 0,5 s. The total resistance of the coil is 2 Ω.

7.1 Calculate the magnitude of the induced emf when the coil moves into the field and is

perpendicular to the field.

7.2 Calculate the magnitude of the induced current.

0 - 0,0259

7. A square wire coil with each side 180 mm, contains 200 turns. The magnetic field through the

centre of the coil changes from 0 T to 0,8 T in 0,5 s. The total resistance of the coil is 2 Ω.7.3 What will the magnitude of the emf be if it takes twice as long to move the coil out of the

magnetic field, i.e. 1 s?

8. One complete loop has a surface of 0,1 m2 and a resistance of 10 Ω. The magnetic field

perpendicular to the surface of the loop originally has a magnitude of 0,2 T and decreases to

zero in a time of 10-4 s. Calculate the following:

8.1 The induced emf

8. One complete loop has a surface of 0,1 m2 and a resistance of 10 Ω. The magnetic field perpendicular to

the surface of the loop originally has a magnitude of 0,2 T and decreases to zero in a time of 10-4 s.

Calculate the following:

8.2 The induced current

13. The figure shows a coil with 25 turns and measurements of 0,15 m by 0,2 m. Its plane is perpendicular to

the magnetic field of 0,6 T. The coil rotates 90o in 4,17 x 10-2 s so that its plane is now parallel to the

magnetic field. Calculate the average emf during this time.

2.1 Determine the direction of the induced current and indicate it on each of the sketches.

2.4 The N-pole of a bar magnet enters a coil and

then exits again.

2.4.1 Draw a sketch of the coil where the N-pole is

nearing it and show the induced magnetic field

and the direction of the induced current on it.

2.4.2 Draw a sketch of the coil where the N-pole

exits and show the induced magnetic field and

the direction of the induced current on it.

3.1 The N-pole of a permanent magnet is pushed into the middle of an aluminium ring. It is

found that the ring moves.

Indicate on the diagram the direction of the induced current as well as the direction in which

the ring moves.

6.1 Indicate the direction of the flow of current in each of the three diagrams and the corresponding

position of the needle of the middle-zero galvanometer.

6.2 In each case, say if the acceleration of the magnet is smaller than, bigger than or equal to the

acceleration due to gravity.