Physics Test - ...

The apparent wavelength of light from a star moving away from the earth is \(0.02 \%\) more than the actual wavelength. What is the velocity of star?

What is the conductivity of a pure semiconductor sample if electron density \(=5 \times 10^{12} \) cm\(^{(-3)}\) and hole density \(=8 \times 10^{13} \) cm\(^{(-3)}\) \(\left(\mu_{\mathrm{e}}=2.3 \mathrm{v}^{-1} \mathrm{~s}^{-1} \mathrm{~m}^{2}\right.\) and \(\left.\mu_{\mathrm{h}}=0.01 \mathrm{v}^{-1} \mathrm{~s}^{-1} \mathrm{~m}^{2}\right)\)

A parallel plate capacitor consists of circular plates with radius \(10 {~cm}\), separated by a distance of \(0.5 {~mm}\). The capacitor is charged by an external source such that the electric field between the plates changes at a rate \(5 \times 10^{13} \mathrm{Vm}-1 \mathrm{~s}-1\). The displacement current through the capacitor is:

A convex lens with refractive index \(1.8\) will have maximum focal length in:

The efficiency of a Carnot engine depends on:

If the electrical conductivity of a semiconductor increases when electromagnetic radiation of a wavelength shorter than \(2480\) nm is incident on it. What is the bandgap (in eV) for the semiconductor? 

A stone hangs from the free end of a sonometer wire whose vibrating length when tuned to a tuning fork, is 40 cm. When the stone hangs wholly immersed in water, the resonant length is reduced to 30 cm. The relative density of the stone is:

In a steady flow reversible adiabatic process, work done is equal to:

The minimum energy required to eject an electron, from the metal surface is called: