362781
A magnetic needle suspended parallel to a magnetic field require \(\sqrt 3 \,J\) of work to turn it through \(60^{\circ}\). The torque needed to maintain the needle in this portion will be
1 \(2\sqrt 3 \,J\)
2 \(3\,J\)
3 \(\sqrt 3 \,J\)
4 \(\dfrac{3}{2} J\)
Explanation:
\(W=U_{f}-U_{i}=M B\left[\cos 0^{\circ}=\cos 60^{\circ}\right]\) \(\Rightarrow \dfrac{M B}{2}=\sqrt{3} J\) \(\Rightarrow M B=2 \sqrt{3} J\) Torque required, \(\tau=M \times B=M B \sin 60^{\circ}\) \( = 2\sqrt 3 \times \frac{{\sqrt 3 }}{2} = 3\;J\) So, correct option is (2)
AIIMS - 2019
PHXII04:MOVING CHARGES AND MAGNETISM
362782
Work done on electron moving in a solenoid along its axis is equal to
1 zero
2 \(e v B\)
3 ilB
4 None of these
Explanation:
Net force acting on electron is zero as \(F_{m}=e v B \sin 0^{\circ}=0\) Hence, work done \(=\) zero .
362781
A magnetic needle suspended parallel to a magnetic field require \(\sqrt 3 \,J\) of work to turn it through \(60^{\circ}\). The torque needed to maintain the needle in this portion will be
1 \(2\sqrt 3 \,J\)
2 \(3\,J\)
3 \(\sqrt 3 \,J\)
4 \(\dfrac{3}{2} J\)
Explanation:
\(W=U_{f}-U_{i}=M B\left[\cos 0^{\circ}=\cos 60^{\circ}\right]\) \(\Rightarrow \dfrac{M B}{2}=\sqrt{3} J\) \(\Rightarrow M B=2 \sqrt{3} J\) Torque required, \(\tau=M \times B=M B \sin 60^{\circ}\) \( = 2\sqrt 3 \times \frac{{\sqrt 3 }}{2} = 3\;J\) So, correct option is (2)
AIIMS - 2019
PHXII04:MOVING CHARGES AND MAGNETISM
362782
Work done on electron moving in a solenoid along its axis is equal to
1 zero
2 \(e v B\)
3 ilB
4 None of these
Explanation:
Net force acting on electron is zero as \(F_{m}=e v B \sin 0^{\circ}=0\) Hence, work done \(=\) zero .
