The current changes in a coil from 10 A to 2 A in 0.2 s. The induced emf produced is 50 V. The self inductance of the coil is:

A cell of constant emf is first connected to a resistance \( R_1 \) and then connected to a resistance \( R_2 \). If power delivered in both cases is same, then the internal resistance of the cell is

X-rays of wavelength, \(\lambda=r{A}\) have frequency :

The energy of a photon of wavelength (\( \lambda \)) is given by the expression: (Symbols have their usual meaning: h = Planck's constant, c = speed of light)

Below given are some statements about electronic devices:
(A) Diodes can be used for rectifying an ac voltage.
(B) For semiconductors, band gap energy \( E_g > 3 \, eV \).
(C) By changing the external applied voltage, junction barriers can be changed.
(D) p-n junction is the 'key' to all semiconductor devices.
Choose the correct answer from the options given below:

Three identical resistors are connected first in series to an electrical voltage V. Let I be the total current flowing in the circuit. These resistors are disconnected and again connected in parallel with the same source. Which of the following statements are true?
(A) The potential difference across each resistor is V/3 in series connection
(B) The potential difference across all three resistors in parallel connection is 3V
(C) The current flowing in each resistor in series connection is the same as I
(D) The current flowing through each resistor in parallel combination is equal to 31
Choose the correct answer from the options given below:

An electric dipole is placed parallel to the electric field. If W is the work done in rotating the dipole by \(30^\circ\), then work done in rotating it by \(180^\circ\) is:

If \(y=2 x(x-1)(2-x)\); then \(\frac{d^2 y}{d x^2}\) is:

How many episodes of mass extinctions of species have occurred on earth since the origin and diversification of life?

Let \(\tan ^{-1} y=\tan ^{-1} x+\tan ^{-1}\left(\frac{2 x}{1-x^2}\right)\). Then \(y\) is :

The chromosome numbers in the gamete of fruit fly is:

The value of integral \(\int \sqrt{4 x^2+9} d x\) is

Which of the following is the correct equation to find the area of the shaded region, with reference to the figure given below ?