Magnetic Effects of Current - NEET Physics Chapterwise MCQs & PYQs
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NEET Magnetic Effects of Current MCQs & PYQs
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Question 181:
easy
Assertion (A): The properties of paramagnetic and ferromagnetic substances are not affected by heating.
Reason (R): As temperature changes, the alignment of molecular magnets does not change.
The magnetic properties of paramagnetic and ferromagnetic substances are strongly affected by temperature. Paramagnetic susceptibility is temperature-dependent (Curie's Law), and ferromagnets become paramagnets above their Curie temperature. Thermal agitation due to heating disorients molecular magnets. Both Assertion (A) and Reason (R) are false.
Assertion (A): Soft iron is used as transformer core.
Reason (R): Soft iron has narrow hysteresis loop.
Soft iron is preferred for transformer cores because its narrow hysteresis loop indicates low energy loss (heat) during repeated cycles of magnetisation and demagnetisation. This property is crucial for efficient transformer operation. Both Assertion and Reason are true, and Reason is the correct explanation of the Assertion.
A uniform electric field and a uniform magnetic field are acting along the same direction in a certain region. If an electron is projected in the region such that its velocity is pointed along the direction of fields, then the electron
The magnetic force on the electron is \(F_m = q(\vec{v} \times \vec{B}) = 0\) since they are parallel. The electric force is \(F_e = -eE\), which acts opposite to its velocity, causing the electron to decelerate and decrease its speed.
A long straight wire of length 2 m and mass 250 g is suspended horizontally in a uniform horizontal magnetic field of 0.7 T. The amount of current flowing through the wire will be (\(g = 9.8 \text{ms}^{-2}\))
For horizontal equilibrium, the upward magnetic force balances the weight: \(I L B = m g ⇒ I = \frac{mg}{LB} = \frac{0.25 \times 9.8}{2 \times 0.7} = 1.75 \text{A}\).
A charge particle having mass \(m\) and charge \(q\) moving with speed \(v\) in uniform transverse magnetic field \(B\). The radial acceleration of charge particle will be
The magnetic force provides the necessary centripetal force: \(F = qvB = m a_r\). Thus, the radial acceleration is \(a_r = \frac{qvB}{m}\).
Two long thin parallel wires separated by a distance \(d\) are carrying a current \(i\) each. The magnitude of the force per unit length applied by one wire on the other is
The magnetic force per unit length between two parallel current-carrying wires is given by \(F/L = \frac{\mu_0 i_1 i_2}{2\pi d}\). Since \(i_1 = i_2 = i\), \(F/L = \frac{\mu_0 i^2}{2\pi d}\), which is directly proportional to \(i^2\).
A charged particle is moving on circular path with velocity \(v\) in a uniform magnetic field \(B\). If velocity of the particle and strength of magnetic field is doubled, then time taken to complete one revolution becomes
The time period of revolution in a magnetic field is \[T = \frac{2\pi m}{qB}\]. It is independent of the velocity \(v\) and inversely proportional to \(B\). Thus, doubling \(B\) makes the time period half of its initial value.
A material suitable for making electromagnets should have
An electromagnet should become strongly magnetized when current is on, and lose its magnetization quickly when current is off. Therefore, it requires high retentivity and low coercivity.
A charged particle moves in a circular path under the action of uniform transverse magnetic field. Which of the given statement should be correct based on above information?
In a uniform magnetic field, the magnetic force is always perpendicular to velocity. Hence, work done is zero and kinetic energy remains constant. However, direction of velocity changes continuously, so momentum changes.