Single Choice

When the electron in the discharge tube is accelerated to high speeds

Athe charge on the electron will decrease.
Bthe specific charge will decrease.
Correct Answer
Cthe charge of the electron will increase.
Dthe value of e/m will increase.

Solution

When sufficient amount of potential (V) is applied between the two electrodes, electrons emitted from the cathode accelerate with velocity v.

$$eV=\dfrac {mv^2}{2}$$\Rightarrow \dfrac{e}{m}= \dfrac{v^2}{2V}$$

So the specific charge of an electron (e/m) is related to potential difference (V) between the cathode and the anode as $$\dfrac{e}{m}\propto\dfrac{1}{V}$$.

Now when the electron in the discharge tube is accelerated to high speeds then the collection rate of anode also increase and result in a decrease of the specific charge.

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