A long wire carrying a steady current is bent into a circular loop of one turn. The magnetic field at the centre of the loop is B. It is then bent into a circular coil of n turns. The magnetic field at the centre of this coil of n turns will be
$B = \dfrac{\mu_0i}{2R} = \dfrac{\mu_0i(2\pi)}{2l} = \dfrac{\mu_0\pi i}{2l}$
$B = \dfrac{\mu_0ni}{2r} = \dfrac{\mu_0ni}{2\left(\dfrac{l}{2n\pi}\right)} = \dfrac{n^2\mu_0\pi i}{2l} = n^2B$
|
A bar magnet is hung by a thin cotton thread in a uniform horizontal magnetic field and is in equilibrium state. The energy required to rotate it by 60º is W. Now the torque required to keep the magnet in this new position is |
Answer |
|
An electron is moving in a circular path under the influence of a transverse magnetic field of 3.57 × 10–2 T. If the value of e / m is 1.76 × 1011 C / kg, the frequency of revolution of the electron is |
Answer |
|
Which of the following combinations should be selected for better tuning of an L–C–R circuit used for communication? |
Answer |
|
A uniform magnetic field is restricted within a region of radius r. The magnetic field changes with time at a rate $\dfrac{d\overrightarrow{B}}{dt}$. Loop 1 of radius R > r encloses the region r and loop 2 of radius R is outside the region of magnetic field as shown in the figure below. Then the e.m.f. generated is |
Answer |
|
The potential differences across the resistance, capacitance and inductance are 80 V, 40 V and 100 V respectively in an L–C–R circuit. The power factor of this circuit is |
Answer |
|
A 100 Ω resistance and a capacitor of 100 Ω reactance are connected in series across a 220 V source. When the capacitor is 50% charged, the peak value of the displacement current is |
Answer |
|
Two identical glass (μg = 3/2) equiconvex lenses of focal length f each are kept in contact. The space between that two lenses in filled with water (μw = 4/3). The focal length of the combination is |
Answer |
|
An air bubble in a glass slab with refractive index 1.5 (near normal incidence) is 5 cm deep when viewed from one surface and 3 cm deep when viewed from the opposite face. The thickness (in cm) of the slab is |
Answer |
|
The interference pattern is obtained with two coherent light sources of intensity ratio n. In the interference pattern, the ratio $\dfrac{I_{max} – I_{min}}{I_{max} + I_{min}}$ will be |
Answer |
|
A person can see clearly object only when they lie between 50 cm and 400 cm from his eyes. In order to increase the maximum distance of distinct vision to infinity, the type and power of the correcting lens, the person has to use will be |
Answer |
