Phy F5 Chap 3 ELECTROMAGNETISM

Diagram 1 shows the cross- section of an electric motor. X and Y are the ends of a coil in which electric current flows. What is the direction of the force exerted on X and Y ?

• Upwards ; Upwards

• Upwards ; Downwards

• Downwards ; Upwards

• Downwards ; Downwards

Diagram 2 shows a device that uses an electromagnet. Which of the bulbs, P or Q, will be lit when switch S is closed and what is this device known as?

• P ; Electric bell

• P ; Relay

• Q ; Relay

• Q ; Telephone

Diagram 3 shows an electromagnet used to lift some iron nails from a beaker of nails. When the switch S is open, some of the nails fell down, but a few nails remained stuck to the steel core. How must the electromagnet be modified so that when the switch is open, all the nails will fall down?

• Use a soft iron core instead of a steel core

• Reduce the number of turns in the electromagnet

• Move the electromagnet further from the beaker

• Use a cell of lower voltage

Diagram 4 shows a current- carrying conductor in a magnetic field. What is the direction of the force that acts on the conductor?

• A

• B

• C

• D

Diagram 5 shows a copper rod that is moved upwards and downwards between the poles of a permanent magnet. Which of the following method will increase the deflection of the pointer of the galvanometer?

• Reverse the polarity of the magnet

• Use a longer copper rod

• Increase the distance between the two magnets of different polarity

• Use a stronger magnet

Diagram 6 shows a d.c. motor with a commutator. The function of the commutator is

• to change a d.c. to an a.c.

• to change an a.c. to a d.c.

• to reverse the current in the coil every time the coil turns half a cycle

• to reverse the force acting on the coil every time the coil turns half a cycle

Diagram 7 shows an aluminum plate swinging into a magnetic field between two poles of a permanent U magnet. The plate comes to a stop after swinging about 3 times. Which of the following is not true about this situation?

• Induced currents flow in the aluminum plate while swinging in the magnetic field.

• Faraday's law explains why the plate comes to a stop fast.

• There will be no change if the N and S poles of the magnet are reversed.

• If a wooden plate was used instead of the aluminum plate, it will take longer time to stop.

Diagram 8 shows two graphs, P and Q. Graph P represents the output of an a c, generator. If it is modified by adding a certain component, the output becomes as shown in graph Q. What is this component?

• Slip rings

• Rheostat

• Electromagnetic relay

• Split ring commutator

Diagram 9 shows the graph of the output voltage against time for an a.c. generator. If the generator is rotated twice as fast, which of the following will be the output voltage?

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Diagram 10 shows an electronic appliance used to charge a smartphone Which transformer can installed in the appliance?

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