$A$ stick of $1 \, m$ is moving with a velocity of $2.7 \times 10^8 \, m/s$. What is the apparent length of the stick in meters? (Given: $c = 3 \times 10^8 \, m/s$)

$1 \ J$ is equal to how many electron volt?

$A$ photodiode sensor is used to measure the output of a $300 W$ lamp kept $10 m$ away. The sensor has an opening of $2 cm$ in diameter. How many photons enter the sensor if the wavelength of the light is $660 nm$ and the exposure time is $100 ms$? (Assume that all the energy of the lamp is given off as light and $h = 6.6 \times 10^{-34} J s$)

There are two sources of light,each emitting with a power of $100 \, W$. One emits $X$-rays of wavelength $1 \, nm$ and the other visible light at $500 \, nm$. Find the ratio of the number of photons of $X$-rays to the photons of visible light of the given wavelength.

If $h$ is Planck's constant in $SI$ system,the momentum of a photon of wavelength $0.01 \, \mathring{A}$ is:

The ratio of the energy of a photon with $\lambda = 150\,nm$ to that with $\lambda = 300\,nm$ is