Magnetism and electromagnetism – Notes and Questions & Answers
Magnetic Filed Lines
A compass needle always points in the North-South direction and is used to plot the direction of magnetic lines of force. Since unlike poles attract the North indicator of the compass needle will point to the South of the bar magnet. Field lines run from North pole to South pole outside the bar magnet and from South pole to North pole inside the bar magnet.
Multiple Choice Questions on Magnetism
The phenomenon related to attractive and directive properties is:
Answer: magnetism
Attraction is the surest test of magnetism:
Answer: False
Like poles of a magnet repel each other:
Answer: True
Materials which are attracted by magnets are:
Answer: ferromagnetic
Which is not a ferromagnetic material:
Answer: glass
Which is a ferromagnetic material:
Answer: cobalt
Which is not a property of a magnet:
Answer: assertive
In a magnet, the attraction is strongest:
Answer: at poles
Freely suspended magnet points in ____ direction.
Answer: north-south
Iron loses its magnetism easily.
Answer: True
Steel is a hard magnetic material.
Answer: True
A freely suspended magnet always points in north-south direction. This proves its:
Answer: directive property
Pick the pair of magnetic substances.
Answer: nickel and cobalt
An example of a natural magnet is:
Answer: lodestone
For a given magnet :
Answer: both have the same strength
The magnetic lines of force of a bar magnet are:
Answer: continuous and non intersecting
Strength of magnetic field is shown by the density of magnetic lines of force.
Answer: True
Magnetic field is strong at the place where magnetic lines of force are:
Answer: dense
A magnetic material acquires temporary magnetic property in presence of another magnet near it due to:
Answer: induced magnetism
During magnetic induction, a magnetic pole induces _____ polarity on the near end of iron bar being induced.
Answer: opposite
The direction of magnetic field at a point on a magnetic field line is given by:
Answer: tangent
What kind of magnetic field is represented by parallel and equidistant lines?
Answer: uniform magnetic field
Several soft iron pins cling one below the other from the pole of a magnet due to:
Answer: induced magnetism
The field around a bar magnet is:
Answer: non uniform
Earth’s magnetic field at a small horizontal plane on the earth’s surface is:
Answer: uniform
Which is a magnetic material?
Answer: steel
Which is a magnetic material?
Answer: iron
Which is a non magnetic material?
Answer: zinc
Which is a non magnetic material?
Answer: magnesium
How can you find out which end of a magnet is the north pole?
Answer: put it near a compass
Electromagnetism – How to identify the North and South poles of an electromagnet?
When a copper wire is coiled in shape of a cylinder (solenoid) and current passed, it forms an electromagnet. The magnetic field produced resembles that of bar magnet. To identify the north and south pole, turn the electromagnet so that one end faces the eye. Remember current flows from positive to negative terminal.
If you observe electric current is flowing clockwise then that end of the solenoid is SOUTH pole.
Observe ‘ S ‘ is written showing clockwise direction
If you observe the current is flowing anti-clockwise then that end of the solenoid is NORTH pole.
Observe ‘ N ‘ is written showing clockwise direction
Multiple Choice Questions on Electromagnetism
Solenoid with soft iron core is:
Answer: electromagnet
A coil wound over soft iron piece is:
Answer: solenoid
An electro magnet is:
Answer: temporary magnet
When current through coil stops flowing, the coil remains an electromagnet.
Answer: False
Iron is used to make permanent magnet.
Answer: True
The magnetic field around a current carrying coil:
Answer: Lasts as long as current flows
Strength of magnetic field in solenoid can be increased by:
Answer: increasing the number of turns
Strength of magnetic field in solenoid can be increased by:
Answer: increasing current strength.
Strength of magnetic field in solenoid can be increased by:
Answer: increasing current strength
Which is not a use of electromagnet:
Answer: study of mechanical properties
Strength of an electromagnet can be determined using:
Answer: magnetic compass
Which of the following uses electromagnetic effect?
Answer: washing machine
If current direction flowing through a wire is reversed the direction of magnetic field will:
Answer: will get reversed
What is the difference between permanent magnet and electromagnet?
Answer: Electromagnets can be turned off
The polarity of an electromagnet can be reversed by reversing the direction of current in the solenoid.
Answer: True
The magnetic polarity at the two ends of a horse shoe electromagnet depends on:
Answer: direction of current at the two ends
What kind of magnet can be turned on and off?
Answer: Electromagnet
Multiple Choice Questions on Electric Bell
A device that works on the basis of magnetic effects of current is:
Answer: electric bell
In an electric bell electrical energy is finally converted into:
Answer: sound energy
Electric bell is application of:
Answer: electromagnet and magnetic effect of current
Which is incorrect for working of electric bell?
Answer: the bell rings when switch is not pressed
In an electric bell, when electromagnet is demagnetised, the hammer strikes the gong.
Answer: False
On magnetisation of electromagnet the hammer of electric bell strikes the gong.
Answer: True
Magnet used in electric bell is:
Answer: horse shoe electromagnet
In an electric bell when the electromagnet attracts the armature, it demonstrates conversion of electrical energy to:
Answer: mechanical energy
In an electric bell when the armature hits the gong, it demonstrates conversion of electrical energy to:
Answer: sound energy
In an electric bell to increase the volume of sound you have to:
Answer: increase current flowing through circuit
The purpose of armature in electric bell is to:
Answer: make and break circuit
What brings back the armature to original position when circuit is broken?
Answer: spring
The frequency of ringing of an electric bell can be altered by adjusting:
Answer: hammer and armature