The corpuscle was discovered using cathode rays. A. True, the corpuscle was disc

Question

The corpuscle was discovered using cathode rays. A. True, the corpuscle was discovered using cathode rays. B. False, the corpuscle was discovered using cathode ray tubes. The corpuscle, now known as the electron, was discovered one hundred years ago by British Physicist, J.J. Thomson 100 years ago at the Cavendish Laboratory at Cambridge University. A. False B. True Measurement of e/m was possible because of instrument made by A JJ Thomson B. J Perrin C. Edison D. Bohr Smallest charge of the -ve cathode ray particles which was observed by Millikan was A. 1.60 times 10^-19 B. 1.90 times 10^-19 C. 1.30 times 10^-19 D. 1.21 times 10^-19

Explanation / Answer

mcq13

answer A is correct

Cathode rays (also called an electron beam or e-beam) are streams of electrons observed in vacuum tubes

mcq14

option B is correct

Electrons were discovered as the constituents of cathode rays. In 1897 British physicist J. J. Thomson showed the rays were composed of a previously unknown negatively charged particle, which was later named the electron. Cathode ray tubes (CRTs) use a focused beam of electrons deflected by electric or magnetic fields to create the image in a classic television set. Cathode rays are made up of negatively charged particles.

mcq15

option correct is not there   (A)

J. J. Thomson measured the charge-by-mass-ratio (e/m) of cathode ray particle using deflection in both electric and magnetic field.

em=1.76×108

coulomb per gram

The cathode ray particle turned out to be 2000 times lighter than hydrogen.

Although we got e/m ratio for electron from J.J. Thomson’s Cathode Ray Tube experiment, we still don’t know the exact charge (e) for electron. American physicist Robert Millikan designed an experiment to measure the absolute value of the charge of electron which is discussed below.

mcq16

option A is correct

What Millikan did was to put a charge on a tiny drop of oil, and measure how strong an applied electric field had to be in order to stop the oil drop from falling. Since he was able to work out the mass of the oil drop, and he could calculate the force of gravity on one drop, he could then determine the electric charge that the drop must have. By varying the charge on different drops, he noticed that the charge was always a multiple of -1.6 x 10 -19 C, the charge on a single electron. This meant that it was electrons carrying this unit charge.

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