Why do we use low pressure in discharge tube?

You need the low pressure in the tube so that the passage of the beam of electrons is not impeded very much by collision with air molecules. You need a reasonably high accelerating voltage to give the electrons enough kinetic energy to make the fluorescent screen glow when the electrons hit the screen.

Why was gas at low pressure taken by Thomson while conducting the experiment?

The cathode ray tube doesn’t conduct electricity per se. It liberates free electrons that are simply moving through a vacuum from one end to the other. In practice, you can’t create a real vacuum, so a low pressure gas (as low as possible) is used instead.

Why does electric discharge not occur at very low pressure?

When the gas pressure is very low there are few gas atoms in the discharge tube. As such there is no hindrance to the movement of electrons and the gas conducts electricity. When the gas atoms in the discharge tube are at atmospheric pressure they collide with the electrons preventing them from reaching the anode.

What is the pressure in discharge tube?

—The increase in pressure of a gas in a discharge tube due to the discharge has been measured for pressures from about 0.1 to 20 mm of mercury for helium, hydrogen, oxygen, nitrogen, air, carbon monoxide and carbon dioxide.

Why a very high voltage is used in cathode ray tube?

High voltage was used for rapid flow of electrons , so that they posses much energy that they can displace electrons of hydrogen atom during collision, hence cathode ray particles/electrons are produced and then attracted towards the anode.

What is the pressure inside cathode ray tube?

The first true electronic vacuum tubes, invented in 1904 by John Ambrose Fleming, used this hot cathode technique, and they superseded Crookes tubes. These tubes didn’t need gas in them to work, so they were evacuated to a lower pressure, around 10−9 atm (10−4 Pa).

What should be the pressure inside the cathode ray tube to obtain cathode rays?

In cathode ray discharge tube, any gas can be taken into the tube. But the gas must be subjected to very low pressure maintained by a vacuum pump and high voltage (10,000V).

Why gases are good conductors at low pressure?

At low pressure molecules of gas are far from each other due to which gas molecules have enough mean free path to accelerate. This means gas particles will acquire enough velocity and hence kinetic energy for the ionization of other molecules. And this is why gases conduct electricity at low pressure.

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

Low pressure means that less number of gas molecules is present in the discharge tube. Moreover, high voltage increases the kinetic energy of the electrons which in turn increases the probability of removal of electrons form the gaseous molecules.

Why the electrical discharge through the gases could be observed only at very low pressure and at very high voltage?

1)It can only be observed so because air is a poor conductor and on such harsh conditions(high voltage and low pressure) air conducts electricity.

What is discharge tube experiment?

In discharge tube experiment, at low pressure and at very high voltage, an electric current is passed. Due to passage of electric current, a stream of rays is passed in the tube originating from cathode. These rays are called “CATHODE RAYS”. These rays originate from cathode.

Why is the study of electric discharge through gases important?

The study of electric discharge through gases gives valuable information regarding the structure of atoms. This has led to the discovery of electrons by J. J. Thomson and later on, to the discovery of X-rays by Roentgen. Discharge of electricity through gases at low pressure – Discovery of electrons

Why does a cathode ray tube need a low pressure?

If the cathode ray experiment has a beam of electrons hitting a fluorescent screen which glows then: You need the low pressure in the tube so that the passage of the beam of electrons is not impeded very much by collision with air molecules.

Why do we need low pressure in a fluorescent tube?

You need the low pressure in the tube so that the passage of the beam of electrons is not impeded very much by collision with air molecules. You need a reasonably high accelerating voltage to give the electrons enough kinetic energy to make the fluorescent screen glow when the electrons hit the screen.

How was the pressure of the gas inside the tube lowered?

The two metal pieces were connected with an external voltage. The pressure of the gas inside the tube was lowered by evacuating the air. Apparatus as set up by providing a high voltage source and evacuating the air to maintain the low pressure inside the tube.