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Question 12 Marks
Two bar magnets are placed close to each other with their opposite poles facing each other. In absence of other force the magnets are pulled towards each other and their kinetic energy increases. Does it contradict our earher knowledge that magnetic forces cannot do any work and hence cannot increase kinetic energy of a system?
Answer
As the magnet come closer to each other thus magnetic fields of lines are more dense and thus more is the force applying to each other. as force increases thus kinetic energy increases.
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Question 22 Marks
Compare the direction of the magnetic field inside a solenoid with that of the field there if the solenoid is replaced by its equivalent combination of north pole and south pole.
Answer
The direction of magnetic field is same in both cases as in solenoid magnetic field lines are directed from on end to other end internally and thus externally. so as in magnet.
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Question 32 Marks
The force on a north pole,$\overrightarrow{\text{F}}=\text{m}\overrightarrow{\text{B}},$ is parallel to the field $\overrightarrow{\text{B}}.$ Does it contradict our earlier knowledge that a magnetic field can exert forces only perpendicular to itself?
Answer
Yes it contradicts as force is always perpendicular to magnetic field. but in case other force is very far distant then the magnetic field can be parallel to force.
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Question 42 Marks
An iron needle is attracted to the ends of a bar magnet but not to the middle region of the magnet. Is the material making up the ends of a bar magnet different from that of the middle region?
Answer
When a iron needle is attracted to towards a magnet. one pole of magnet induces other pole on the nearest side of needle thus making iron needle it self a magnet thus needle is attracted to one side of the magnet.
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Question 52 Marks
Sketch the magnetic field lines for a current-carrying circular loop near its centre. Replace the loop by an equivalent magnetic dipole and sketch the magnetic field lines near the centre of the dipole. Identify the difference.
Answer
As in loop magnetic field lines pass thorough the center but in case of magnet dipole the magnetic field lines does not pass through center or even meet at center point.
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