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Question 52

Electrons in a cathode ray tube have been emitted with a velocity of $$1000 \text{ ms}^{-1}$$. The number of following statements which is/are true about the emitted radiation is
Given: $$h = 6 \times 10^{-34}$$ Js, $$m_e = 9 \times 10^{-31}$$ kg
(A) The deBroglie wavelength of the electron emitted is 666.67 nm
(B) The characteristic of electrons emitted depend upon the material of the electrodes of the cathode ray tube.
(C) The cathode rays start from cathode and move towards anode.
(D) The nature of the emitted electrons depends on the nature of the gas present in cathode ray tube.


Correct Answer: 2

Solution

λ=h/(mv)=6×10⁻³⁴/(9×10⁻³¹×1000)=6×10⁻³⁴/9×10⁻²⁸=0.667×10⁻⁶ m=666.7 nm. (A) TRUE.

(B) Electrons are same regardless of electrode material — FALSE.

(C) Cathode rays go from cathode to anode — TRUE.

(D) Nature of electrons doesn't depend on gas — FALSE.

True statements: A and C = 2.

The answer is $$\boxed{2}$$.

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