Physics
In a physics laboratory, a student places a bar magnet near a compass. At certain positions, the compass needle shows no deflection.
(a) Why does the compass needle show no deflection at certain points? What are these points called?
(b) What happens to the magnetic field lines at these points?
(c) Why are these points useful in studying magnetic fields?
(d) Are these points fixed, or do they change their positions?
Answer
(a) The compass needle shows no deflection at certain points because the magnetic field due to the bar magnet is equal and opposite to the horizontal component of Earth's magnetic field at those points. Hence, the resultant magnetic field becomes zero. These points are called neutral points.
(b) At neutral points, the magnetic field due to the magnet and the horizontal component of Earth’s magnetic field are equal in magnitude and opposite in direction. Therefore, the resultant magnetic field is zero.
(c) Neutral points are useful because they help in determining the strength and direction of magnetic fields. By locating these points, the magnetic field of a magnet can be compared with Earth's magnetic field.
(d) These points are not fixed. Their positions change with the strength and orientation of the magnet and also with the direction and strength of Earth's magnetic field.
Related Questions
Assertion (A) : Two bar magnets attract when they are brought near to each other with the same pole.
Reason (R) : Unlike poles attract each other.
- both A and R are true and R is the correct explanation of A
- both A and R are true and R is not the correct explanation of A
- assertion is false but reason is true
- assertion is true but reason is false
Assertion (A) : Magnetic field lines never intersect each other.
Reason (R) : At a particular point, magnetic field has only one direction.
- both A and R are true and R is the correct explanation of A
- both A and R are true and R is not the correct explanation of A
- assertion is false but reason is true
- assertion is true but reason is false
Assertion (A) : Neutral points are the points at which two magnetic fields are equal in magnitude and in the same direction.
Reason (R) : The net magnetic field at a neutral point is zero.
- both A and R are true and R is the correct explanation of A
- both A and R are true and R is not the correct explanation of A
- assertion is false but reason is true
- assertion is true but reason is false
Ravi observed that an electromagnet could lift iron pieces only when electric current was flowing through it. When the current was switched off, the iron pieces fell down.
(a) Why does an electromagnet lose its magnetism when the current stops?
(b) How is an electromagnet different from a permanent magnet?
(c) How can the strength of an electromagnet be increased?
(d) Why are electromagnets preferred in cranes?
(e) Which material is preferred for making the core of an electromagnet?