Tag: physics

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Questions Related to physics

Multiple choice detection and recording of x-ray images option c: imaging physics

Compton effect is associated with

  1. $\alpha -$ rays
  2. $\beta -$rays

  3. Positive rays

  4. X-rays
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Compton scattering is an inelastic scattering of a photon by a quasi-free charged particle, usually an electron. It results in a decrease in energy (increase in wavelength) of the photon (which may be an X-ray or gamma ray photon), called the Compton effect. Part of the energy of the photon is transferred to the recoiling electron. Binding energy is equal to work function of metal. In most of metals, the threshold frequency is equal to that of ultravoilet light. So Compton effect is associated with X-rays.

Multiple choice detection and recording of x-ray images option c: imaging physics

Which of the following phenomenon supports the quantum nature of light?

  1. Compton effect

  2. Interference

  3. Diffraction

  4. Polarisation
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The wave nature of light is exhibited by interference, diffraction and polarisation of light.
Compton effect is the strongest evidence to show the particle nature of light, and hence the quantum theory of light.

So, the answer is (A).

Multiple choice detection and recording of x-ray images option c: imaging physics

According to photon theory of light which of the following physical quantities  associated with a photon do not / does not change as it collides with an electron is vacuum:

  1. Energy and momentum

  2. Speed and momentum

  3. Speed only

  4. Energy only
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Under the photon theory of light, a photon is a discrete bundle (or quantum) of electromagnetic (or light) energy. Photons are always in motion and, in a vacuum, have a constant speed of light to all observers, at the vacuum speed of light (more commonly just called the speed of light) of $c = 2.998 \times 10^8 m/s$

According to the photon theory of light, photons .
move at a constant velocity, $c = 2.9979 \times 10^8 m/s$ (i.e. "the speed of light"), in free space
have zero mass and rest energy.

Carry energy and momentum, which are also related to the frequency $\mu$ and wavelength $\lambda$ of the electromagnetic wave by $E = h \mu$ and $p = \dfrac{h}{\lambda}.$

Can be destroyed/created when radiation is absorbed/emitted.

Can have particle-like interactions (i.e. collisions) with electrons and other particles, such as in the Compton effect
Multiple choice detection and recording of x-ray images option c: imaging physics

The apparent wavelength of the light from a star moving away from the earth is 0.2% more than its actual wavelength. Then the velocity of the star is 

  1. $6 \times 10^7 \ ms^{-1}$
  2. $6 \times 10^6 \ ms^{-1}$
  3. $6 \times 10^5 \ ms^{-1}$
  4. $6 \times 10^4 \ ms^{-1}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The Doppler shift formula for light is delta_lambda / lambda = v / c. Given delta_lambda / lambda = 0.2% = 0.002, then v = 0.002 * c. Using c = 3 * 10^8 m/s, v = 0.002 * 3 * 10^8 = 6 * 10^5 m/s.

Multiple choice detection and recording of x-ray images option c: imaging physics

From the $\alpha$-particle scattering experiment, Rutherford concluded that

  1. $\alpha$- particles can come within a distance of the order of $10^{-14}$ m of the nucleus.
  2. The radius of the nucleus is less than $10^{-14}$ m

  3. Scattering follows coulomb's law

  4. The positively charged parts of the atom move with extremely high velocities
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Rutherford's alpha-particle scattering experiment allowed him to estimate the distance of closest approach, which provided an upper bound for the radius of the nucleus, concluding it is less than 10^-14 m.

Multiple choice detection and recording of x-ray images option c: imaging physics

X-rays of wavelength of $22\ pm$ are scattered from a carbon target at an angle of $85^0$ to the incident beam. The compton shift for X-rays is $(cos\ 85^0=0.088)$

  1. $2.2\ pm$
  2. $1.1\ pm$
  3. $0.55\ pm$
  4. $4.4\ pm$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Compton shift is given as $\Delta \lambda =\dfrac{h}{mc}(1-cos \phi )=\dfrac{6.62\times 10^{-34}Js}{9.1\times 10^{-31} Kg\times 3\times 10^8m/s}(1-cos 85^0)$ 

where $m$ is the mass of electron and $h$ is Planck's constant with $c$ as speed of light in air.
On calculation we get the shift as $\Delta \lambda =2.2\times 10^{-12}meter=2.2pico meter$
Option A is correct.

Multiple choice detection and recording of x-ray images option c: imaging physics

Find the correct statement

  1. A free electron can absorb a photon completely.

  2. A free electron can not absorb a photon completely.

  3. A free electron can not exist.

  4. A free neutron can exist for a long time
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to Compton's scattering 


$\displaystyle \Delta \lambda =\dfrac{h}{mc}(1-\cos \phi )$ 

which shows a free electron can not absorb a photon completely. If a free electron absorb a photon there is nothing to share the recoil. So momentum will not conserve which is not possible.
So, the answer is option (B).

Multiple choice detection and recording of x-ray images option c: imaging physics

For Compton effect with visible light the observed Compton shift is

  1. Very large because the electrons appear free

  2. Very small because the electrons appear free

  3. Is almost zero because the electrons appear bound

  4. Less than zero
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In compton scattering it is necessary that the energy of the photon should be very much greater than binding energy of electron. Binding energy is equal to work function of metal. In most of metals, the threshold frequency is equal to that of ultravoilet light that is why we do not observe comption effect with visible light.