Electromagnet - class-VIII
Comprehensive quiz on electromagnets covering their construction, working principles, magnetic properties, and practical applications for class VIII students.
Questions
A permanent magnet in the shape of a thin cylinder of length $10$cm has magnetisation (M) $=10^6$A $m^{-1}$. It's magnetization current $I _M$ is?
- $10^5$A
- $10^6$A
- $10^7$A
- $10^8$A
The strength of an electromagnet can be increased by.
- increasing the current in the coil
- decreasing the current in the coil
- decreasing the number of turns in the coil
- increasing the length of air gap between its poles
For making a strong electromagnet, the material of the core should be
- soft iron
- steel
- brass
- copper
strength of electromagnet increases when
- the number of turns in the coil increases
- the current flowing in the coil increases
- both a and b
- the number of turns in the coil decreases
Two electromagnets are made by wrapping a few turns of wire on similar nails and passing the same amount of electric current through them.The number of turn of the wire wrapped over the two iron nails are in the ratio 2:1.The strength of
- The first electromagnet will be greater
- The second electromagnet will be greater
- Both the electromagnets will be equal
- Electromagnets has no relation with the number of turns
An example of a perfect diamagnet is a superconductor . This implies that when a superconductor is put in a magnetic field of intensity $B$, the magnetic field ${B _s}$ inside the superconductor will be such that:
- ${B _s} = - B$
- ${B _s} = 0$
- ${B _s} = B$
- ${B _s} < B but\,{B _s} \ne 0$
One bar magnet and one coil both are in a steady state. North pole of the magnet is towards the coil, then this end of the coil becomes.
- north pole
- south pole
- have no magnetic pole
- north and south pole any of that
The phenomeno of paramagnetism is a consequnce of
- Distortion effect.
- Orientation effect
- Both (A) and (B)
- Neither (A) nor (B)
Complete the given statement, the strength of an electromagnet can be:
- increased by adding a ferromagnetic core
- decreased by adding turns of wire to the coil
- increased by reducing the current through the wire
- increased by adding an aluminum core
- decreased by adding more layers of wire to the coil
When a magnet is moved with its south pole towards a closed coil, the nearer end of the coil acts like a
- South pole
- North pole
- Either $(1)$ or $(2)$
- Neither $(1)$ or $(2)$
Electromagnets are used in
- Electric bells
- Telephones
- Dynamos
- All of these
Electromagnets are used in
- electric bells only
- telephones only
- dynamos only
- all the above
Electromagnets are used in
- electric bells only.
- telephones only.
- dynamos only.
- all the above.
In which of the following devices is an electromagnet used?
a. Electric tram
b. Loud speaker
c. Telegraph
d. Relay microphone
- a
- b, c and d
- a and b
- All of the above
Match the following
| 1. Industrial use | a. Study of magnetic properties under magnetic field |
|---|---|
| 2. Scientific use | b. Removing pieces of iron from wounds |
| 3. Medical use | c. To separate iron filaments from other waster |
| 4. Easiest method | d. Lifting and transporting heavy loads of iron mass |
- $1-d, 2-a, 3-b, 4-c$
- $1-b, 2-d, 3-c, 4-a$
- $1-c, 2-b, 3-a, 4-d$
- $1-a, 2-c, 3-d, 4-b$
When the current through the electromagnet of a relay reaches a particular value.
- It breaks the circuit
- It opens the circuit by pulling in an iron contact
- It closes the circuit by pulling in an iron contact
- Both A or C