Class 10 - Physics - Magnetic Effects of Electric Current
Which of the following correctly describes the magnetic field near a long straight wire?
(a) The field consists of straight lines perpendicular to the wire.
(b) The field consists of straight lines parallel to the wire.
(c) The field consists of radial lines originating from the wire.
(d) The field consists of concentric circles centred on the wire.
Correct option: - (d) the field consists of concentric circles centred on the wire.
According to right hand thumb rule the magnetic field lines, produced around a straight current - carrying are concentric circles.
The phenomenon of electromagnetic induction is
(a) the process of charging a body.
(b) the process of generating magnetic field due to a current passing through a coil.
(c) producing induced current in a coil due to relative motion between a magnet and the coil.
(d) the process of rotating a coil of an electric motor.
Correct option: - (c) producing induced current in a coil due to relative motion between a magnet and the coil.
When a straight coil and a magnet are moved relative to each other, a current is induced in the coil. This phenomenon is known as electromagnetic induction.
The device used for producing electric current is called a
Correct option: - (a) generator.
An electric generator produces electric current. It converts mechanical energy into electricity.
The essential difference between an AC generator and a DC generator is that
(a) AC generator has an electromagnet while a DC generator has permanent magnet.
(b) DC generator will generate a higher voltage.
(c) AC generator will generate a higher voltage.
(d) AC generator has slip rings while the DC generator has a commutator.
Correct option: - (d) AC generator has slip rings while the DC generator has a commutator.
An AC generator has two rings called slip rings. A DC generator has two half rings called commutator.
At the time of short circuit, the current in the circuit
(a) reduces substantially.
(b) does not change.
(c) increases heavily.
(d) vary continuously.
Correct option (c )Increases heavily.
At the time of short circuit, the amount of current in the circuit increases abruptly.
State whether the following statements are true or false.
(a) An electric motor converts mechanical energy into electrical energy.
(b) An electric generator works on the principle of electromagnetic induction.
(c) The field at the centre of a long circular coil carrying current will be parallel straight lines.
(d) A wire with a green insulation is usually the live wire of an electric supply.
List three sources of magnetic fields.
The sources of magnetic fields are following:-
How does a solenoid behave like a magnet? Can you determine the north and south poles of a current–carrying solenoid with the help of a bar magnet? Explain.
A solenoid is formed of long coil of circular loops of insulated copper wire.
When a current is allowed to flow through it, magnetic field lines are produced around the solenoid.
The magnetic field produced by it is similar to the magnetic field of a bar magnet.
When the north pole of a bar magnet is brought near the end connected to the negative terminal of the battery, the solenoid repels the bar magnet.
Since like poles repel each other, the end connected to the negative terminal of the battery behaves
as the north pole of the solenoid and the other end behaves as a south pole.
Therefore one end of the solenoid behaves as a north pole and the other end behaves as a south pole.
When is the force experienced by a current–carrying conductor placed in a magnetic field largest?
The force experienced by a current–carrying conductor placed in a magnetic field largest when the direction of magnetic field
and electric current are perpendicular to each other.
Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall
towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?
The magnetic field inside the chamber is perpendicular to the direction of current and direction of force i.e. either upward or downward. T
he direction of current is given from the front wall to the back wall because negatively charged electrons are moving from back to front wall.
The direction of magnetic force is rightwards. Hence, by using Fleming’s left hand rule, it can be concluded that the direction of magnetic field inside the chamber is downward.
Draw a labelled diagram of an electric motor. Explain its principle and working.
What is the function of a split ring in an electric motor?
Electric motor is a device that converts electrical energy to mechanical energy.
It is used in electric fans, refrigerators, mixers etc.
Name some devices in which electric motors are used.
Devices in which electric motors are used are as flows:-
A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil,
(ii) withdrawn from inside the coil, (iii) held stationary inside the coil?
Two circular coils A and B are placed close to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.
When the two circular coils are placed close to each other, when a current in coil A changes, the magnetic field associated with it also changes.
As a result magnetic field around coil B also changes. This change in magnetic field lines around coil B induces an electric current in it.
This is known as electromagnetic induction.
State the rule to determine the direction of a (i) magnetic field produced around a straight conductor-carrying current,
(ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and
(iii) current induced in a coil due to its rotation in a magnetic field.
Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?
When does an electric short circuit occur?
Electric shocks occur when the insulation wire gets damaged, and when the live wire and the neutral wire touch each other, the current flowing in the circuit increases.
Also if the resistance of the electric circuit is very low, the current flowing through the circuit increases as a result electric shock can occur.
What is the function of an earth wire? Why is it necessary to earth metallic appliances?
The main function of earthing wire is to transfer any current which is getting leaked from an electrical appliance to the ground.
The metallic body of electrical appliance is connected to the earth wire so that any leakage of electric current is transferred to the ground.
This prevents severe shock to the user. That is why earthing of the electrical appliance is necessary.