At an incident radiation frequency of $v_1$, which is greater than the threshold frequency, the stopping potential for a certain metal is $V_1$. At frequency $2v_1$ the stopping potential is $3V_1$. If the stopping potential at frequency $4v_1$ is $n{V}_1$, then $n$ is

Thermopile Bolometer is used to detect

Consider a wire of length \(L\) with a resistance of \(5 \Omega\). Applying an external force, the wire is elongated such that its length becomes \(3 L\). Assuming, the resistivity and density of the material is unchanged, the resistance of the elongated wire is

The circuit shows two capacitors A and B of capacitances \(\mathrm{C}\) and \(2 \mathrm{C}\) respectively. When they are fully charged, the cell is removed and the capacitors are connected with their plates of opposite polarities touching each other. Then

(a) Charge on \(\mathrm{A}\) is \(\frac{4 \mathrm{CE}}{9}\) (b) Charge on \(\mathrm{B}\) is zero (c) Loss of energy in this process is \(\left(\frac{\mathrm{CE}^2}{3}\right)\) The correct statement \(/ \mathrm{s}\) is/are

A cell of emf \(10 \mathrm{~V}\) and internal resistance \(3 \Omega\) is connected in parallel with another cell of emf \(7 \mathrm{~V}\) and internal resistance \(\frac{3}{5} \Omega\), such that their positive terminals are joined together and so their are negative terminals. Their positive terminals are joined with the negative terminal and their negative terminal is joined with the positive terminal of a third cell of emf \(20 \mathrm{~V}\) with internal resistance \(2 \Omega\). The combination can be replaced by a battery of emf \(E\) and internal resistance \(r\), then the values of \(E\) and \(R\) are respectively

In an experiment, the coefficient of viscosity (in mPa s) of a liquid was determined as 2.62, 2.68, 2.58, 2.57, 2.54 and 2.55. The mean absolute error in the determination of the coefficient of viscosity of the liquid is

The radius of a coil of N turns is R. If the plane of the coil is placed parallel to a uniform magnetic field B, then the flux linked with the coil is

The radiation emitted by a star \(A\) is 10000 times that of the sun. If the surface temperatures of the sun and the star \(A\) are \(6000 \mathrm{~K}\) and \(2000 \mathrm{~K}\) respectively, the ratio of the radii of the star \(A\) and the sun is :

A uniform circular disc of radius \(R\), lying on a frictionless horizontal plane is rotating with an angular velocity ' \(\omega\) ' about is its own axis. Another identical circular disc is gently placed on the top of the first disc coaxially. The loss in rotational kinetic energy due to friction between the two discs, as they acquire common angular velocity is ( \(I\) is moment of inertia of the disc)

A person walks along a straight road from his house to a market \(2.5 \mathrm{~km}\) away with a speed of \(5 \mathrm{~km} / \mathrm{h}\) and instantly turns back and reaches his house with a speed of \(7.5 \mathrm{~km} / \mathrm{h}\). The average speed of the person during the time interval 0 to \(50 \mathrm{~min}\) is \((\mathrm{in} \mathrm{m} / \mathrm{s})\)

X-rays of wavelength \(0.140 \mathrm{~nm}\) are scattered from a block of carbon. What will be the wavelengths of \(X\)-rays scattered at \(90^{\circ}\) ?

The horizontal and vertical displacements \(x\) and \(y\) of a projectile at a given time \(t\) are given by \(x=6 t\) metre and \(y=8 t-5 t^2\) metre. The range of the projectile in metre is

Consider the following statements \(A\) and \(B\) and identify the correct answer A. When a person walks on a rough surface the direction of frictional force exerted by the surface on the person is opposite to the direction of his motion. B. When a cycle is in motion, the force of friction exerted by the ground on the front wheel is in the backward direction