1 Physics -- Electrons

Explain why a discharge tube appears dark when evacuated to very low pressure?

1 Answers

At very low pressure, the density of the gas in the discharge tube becomes very low. As a result, the collision between the electrons emitted by the cathode and the gas molecules are avoided. Due to this, the gas molecules do not get excited. Since the gas molecules are not excited, there are no transitions of the molecules from the excited states to the ground states and hence no light is emitted. Therefore, the discharge tube at very low pressure appears dark.

Why is a metal piece heated up when cathode rays strike it?

When cathode rays strike a metal plate, their kinetic energy is transformed into heat energy, which increases the temperature of the plate.

I need help

1. Can we perform Millikan's experiment with drop of any size?

No, it is not advised to perform Millikan's oil drop experiment with drops of any size due to limitations of experimental accuracy.

When we use a drop of larger size (as compared to microscopic sizes), they will have comparatively higher velocity which is difficult to detect.

Similarly, a large electric field should be applied to move the drop towards the positive terminal against gravity.

Why specific charge for positive rays much smaller that that of cathode rays?

Specific charge is the ratio of a particle's charge to its mass.

Since, the mass of an electron is about 1/1837 times that of the mass of a proton. Its mass is much smaller than the proton.

A positive ray contains alpha particles (doubly ionized He nucleus). Its mass is much larger than that of an electron so, the greater electronic charge has negligible effect as compared to its mass, and the specific charge is much smaller than that of the electrons.

What is the importance of Millikan's oil drop experiment?

Following are the significance of Millikan's oil drop experiment:

It verifies that electronic charge is the smallest possible unit of charge.
It helps to calculate the electronic charge by using the value of the specific charge of electron (e/m).

Is dry and dust free air at atmospheric pressure, conductor of electricity? explain.

What are cathode rays? write their two properties.

Cathode rays are negatively charged streams of particles arising from the cathode of an electric discharge tube at low pressure and high electric potential.

Any two properties of cathode rays are:

They are negatively charged particles so, they suffer deflection in electric and magnetic fields.
They travel with 1/10 of the velocity of light.

Why does electric discharge take place at low pressure and high potential difference?

Write down expression of acceleration of a moving charge Q in a parallel and perpendicular magnetic field.

The expression for the acceleration of a moving charge Q in a magnetic field depends on the direction of the magnetic field relative to the velocity of the charge. Here are the expressions for the acceleration of a moving charge Q in a parallel and perpendicular magnetic field:

1. Parallel Magnetic Field:

If the magnetic field is parallel to the velocity of the charge, the charge experiences a force that causes a centripetal acceleration. The expression for the acceleration (a_parallel) is...

Gases are insulators at ordinary pressure and start conducting at low pressures . Why ?

Gases are insulators at ordinary pressure because the particles are spread out, resulting in weak intermolecular interactions and limited energy transfer. However, at low pressures, the distance between gas particles increases, allowing for ionization and excitation upon collision, leading to the creation of free electrons and ions that can conduct electricity.

What are the applications of electron microscopy in various scientific disciplines?

Calculate the energy of an electron in the n=3 energy level of a hydrogen atom. (Given: Ionization energy of hydrogen = 13.6 eV)

An electron travels at a speed of 2.0 x 10^6 m/s in a magnetic field of 0.5 T. Calculate the force experienced by the electron. (Given: Charge of an electron = -1.6 x 10^-19 C)

How do electrons interact with electromagnetic fields, and what are the consequences of such interactions in fields like optics and electronics?

A beam of electrons is accelerated through a potential difference of 500 V. Determine the final kinetic energy of an electron if its initial kinetic energy was 100 eV. (Given: Elementary charge e =...

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