Question

In an X-ray tube, electrons accelerated through a potential difference of 15000 V strike a copper target. The speed of the emitted X-rays inside the tube is
[e= charge on electron, m=mass of electron, Z= atomic number of target]

• A. $\sqrt{\frac{2\times 2e\times 15000}{m}}$
• B. $\sqrt{\frac{2\times e\times 15000}{m}}$
• C. $\sqrt{\frac{2Ze\times 15000}{m}}$
• D. $3\times {10}^{8}m/s$

Answer 1

The correct option is D $3\times {10}^{8}m/s$

X-rays are obtained when the accelerated electrons interact with the atoms (electrons) in the target material. When a bombarding electron passes close to a nucleus it is deflected. The change of direction means that the electron has been accelerated. An accelerating charged particle emits electro-magnetic radiation. If the acceleration is great enough, the quantum of radiation emitted is an x ray. Since it is an electromagnetic radiation, the speed of the emitted X-rays inside the tube will be the speed of light.