Electromagnetic Effects 1

The diagram shows a locking device.
When the current is switched off, the spring pulls the bar to the right.

Which materials should the coil and the bar be made from?
1. coil: copper; bar: iron
2. coil: copper; bar: copper
3. coil: iron; bar: copper
4. coil: steel; bar: nylon
A cathode-ray ocilloscope is connected to an a.c. generator.

What is the effect on the trace if the generator's speed of rotation is doubled?
1. number of waves on the screen: doubled ; amplitude of waves on the screen: same
2. number of waves on the screen: same ; amplitude of waves on the screen: doubled
3. number of waves on the screen: doubled ; amplitude of waves on the screen: doubled
4. number of waves on the screen: same ; amplitude of waves on the screen: same
A small coil is connected to a sensitive ammeter. The ammeter needle can move to either side of the zero position.
When the magnet is allowed to fall towards the coil, the ammeter needle moves quickly to the right of the zero position.

The magnet moves through the coil.
How does the ammeter needle move as the magnet falls away from the coil?
1. It does not move.
2. It gives a steady reading to the right.
3. It moves quickly to the left of the zero position and then returns to zero.
4. It moves quickly to the right of the zero position and then returns to zero.
The diagram showsa current in a conductor in a magnetic field

What is the direction of the force on the conductor?
1. into the page
2. out of the page
3. towards the N-pole
4. towards the S-pole
Why are slip rings used in an a.c. generator?
1. They connect the coil to the external circuit.
2. They convert mechanical energy into electrical energy.
3. They produce the induced e.m.f.
4. They reduce the friction so that the coil can turn more easily.
When a magnet was pushed towards a solenoid, the meter connected to the solenoid showed a deflection to the right.
When the same magnet was pulled away from the solenoid at a faster speed, what was the deflection on the meter?
1. Greater and to the left
2. Greater and to the right
3. The same and to the left
4. The same and to the right
A permananent magnet moving up and down on the end of a spring induce an e.m.f. in a coil.

Which factor, on its own, would decrease the maximum value of the induced e.m.f.?
1. Increasing the number of turns in the coil
2. Increasing the strength of the magnet
3. Raising the coil
4. Raising the support of the spring
When a magnet is moved into the coil of wire shown, there is a small reading on the sensitive meter.

Which change would increase the size of the reading
1. Pushing the magnet in faster
2. Pulling the magnet out
3. Moving the opposite pole in
4. Unwinding some of the turns of wire
A magnet is pushed horizontally towards a coil of insulated wire, inducing an e.m.f. in the coil.

In which direction does the coil try to move?
1. Away from the magnet
2. Towards the magnet
3. Downwards
4. Upwards
The diagram shows a simple a.c. generator.

Which name is given is given to part X?
1. Axle
2. Carbon brush
3. Magnet
4. Slip ring
Which graph shows the output voltage V against time T for a simple a.c. generator?
1. A
2. B
3. C
4. D
A magnet is inserted in to a coil and voltage is induced across the coil.
Which factor has no effect on the voltage induced?
1. The number of turns in the coil.
2. thr speed of which the magnet is inserted.
3. The strength of the magnet.
4. The thickness of the wire of which the coil is made.
What is correct about the input and output of a transformer when a transformer is used successfully?
1. Input: a.c.; Output: a.c.
2. Input: a.c.; Output: d.c.
3. Input: d.c.; Output: a.c.
4. Input: d.c.; Output: d.c.
Which diagram correctly gives the direction of the induced current when the magnet is moved as shown? In each case, the coil of wire is connected in a complete circuit.
1. A
2. B
3. C
4. D
What is the main function of a basic iron-cored transformer?
1. To change a.c. to d.c.
2. To change to a higher or lower a.c. voltage
3. To provide a constant voltage source
4. To store electrical energy
The diagram shows a coil in which there is a current.

What will happen to the magnetic field when an iron bar is inserted into the coil?
1. It become much stronger.
2. It become slightly weaker.
3. It cahnges direction.
4. It stays the same.
The core of a transformer is used to link the primary coil to the secondary coil.
What type of link is this?
1. Electrostatic
2. Magnetic
3. Mechanical
4. Thermal
Which graph shows how the voltage output of a simple a.c. generator varies with time?
1. A
2. B
3. C
4. D
The core of a transformer is made of iron because the iron is .......................
1. a good electrical conductor
2. cheaper than copper
3. easily magnetised and demagnetised
4. makes a good permenent magnet
A coil is rotated about a horizontal axis XY between two flat-ended magnetic poles as shown.

Which graph shown the e.m.f. E induced in the coil during one complete revolution?
1. A
2. B
3. C
4. D

Electromagnetic Effects 1

Multiple Choice Questions