Science
(a) Explain why the deflection of the compass needle reduced as Mona moved away the compass needle from the current carrying wire.
(b) Mention one thing that could have changed in the circuit of the wire that could increase the deflection of the needle.
(c) Explain with reason how the direction of the magnetic field associated with the wire changes if the polarity of battery reversed.
Electro-Magnetism
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Answer
(a) When an electric current flows through a straight wire, it produces a magnetic field around it and the strength of this magnetic field depends inversely on the distance from the wire. Therefore, when Mona moved the compass needle away from the current-carrying wire, the magnetic field at that point became weaker which reduces the force acting on the compass needle and hence, the deflection of the compass needle also decreased.
(b) As the strength of a magnetic field of a wire depends directly on its current so a higher current produces a stronger magnetic field around the wire, which causes a greater deflection of the compass needle.
(c) If the polarity of the battery is reversed, the direction of the current in the wire also reverses which in turn reverses the direction of the magnetic field around the wire.
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