Electric Motor

Q.

Name five appliances or machines which use an electric motor.

Q.

What is the role of the split ring in an electric motor?

Q.

What is the function of a commutator?

Q.

In a DC motor, the device which is used to change the direction of current through the coil after every half rotation is called

1. armature

2. commutator

3. brushes

4. magnet

Q. Question 11
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?

Q. Which of the following correctly represents a uniform magnetic field?

1. A
2. B
3. C
4. D

Q.

An electric motor converts mechanical energy into electrical energy.

1. True

2. False

Q.

An electric motor works making use of

1. mechanical effect of current

2. chemical effect of current

3. heating effect of current

4. magnetic effect of current

Q.

If the number of turns in the armature coil is doubled, the speed of rotation of the armature coil ___.

1. first increases and then decreases

2. decreases

3. remains same

4. increases

Q.

State True or False: The electric motor works on the principle of Fleming’s Left Hand Rule.

1. True
2. False

Q.

State any three ways of increasing the power of DC motor?

Q.

The primary coil of a transformer contains 100 turns; the secondary has 200 turns. The primary coil is connected to a size AA battery that supplies a constant voltage of 1.5 volts. What voltage would be measured across the secondary coil?

1. 3 volts

2. 0.75 volts

3. 0 volts

4. 1.5 volts

Q.

An electric speaker produces sound if a constant current is made to pass through its coil.

1. An electromagnet to rotate the armature

2. Effectively large number of turns of conducting wire in the current carrying coil

Q.

Question 3
What is the role of split ring in an electric motor?

Q. If electrons are not used up in electrical appliances, what actually happens so that the appliance starts working?

Q. An induction motor is a commonly used electrical machine. What examples of its use are given here?

Q.

The magnitude of the force acting on a current carrying wire placed in a magnetic field in the direction perpendicular to its length depends on ___.

1. strength of magnetic field

2. length of the wire

3. mass of wire

4. current I flowing in the wire

Q.

The direction of rotation of a DC motor, as shown below, is in the clockwise direction.
The direction of the magnetic field is ___.

1. left to right

2. right to left

3. vertically upwards

4. vertically downwards

Q. What kind of energy transformation takes place in the following gadgets. [3]
(a) Steam engine
(b) Electric heater
(c) Electric bulb

Q. Question 2
What is the principle of an electric motor?

Q. Which of the following is an incorrect statement regarding the magnetic field?

1. Inside a magnet, magnetic field lines moves from north to south pole.
2. Outside the magnet, field lines originates from the North pole.
3. Magnetic field lines do not intersect each other.
4. Magnetic field lines form closed loops.

Q. TV is also known as

1. Kinescope
2. Telescope
3. Flouroscope
4. Microscope

Q. Why are magnets with concave shaped poles used in DC motor?What happens if magnets with flat poles are used in it?

Q. When the thumb of a right hand points in the direction of the current, the fingers will curl in the direction of magnetic field lines.

1. True
2. False