Question

Select correct alternative :
Statement -1 : Photoelectric effects supports quantum nature of light because electronic charge of the photoelectron is quantized.
Statement -2 : The number of $\alpha$ and $\beta$ particles emitted when $\begin{array}{c}238\\ 92\end{array}U$ decays into $\begin{array}{c}206\\ 82\end{array}Pb$ is 6 and 8.
Statement - 3: If the angular momentum of a system is constant in magnitude then the torque (if any) acting on the system must be perpendicular to the angular momentum.

• A. FFF
• B. TFT
• C. TFF
• D. FFT

Answer 1

Answer: (D)

The photoelectric effect supports the quantum nature of light due to the quantization of energy . It affects only the movement of electronic charges. so statement 1 is false.
If a $\alpha$ emits from a nuclei , 4 unit mass number and 2 unit atomic number reduce from nuclei. If a$\beta$ emits from a nuclei , 1 unit atomic number increase from nuclei and mass number will unchanged.
If $6\alpha ,8\beta$ emit from $\begin{array}{c}238\\ 92\end{array}U$ , mass number of final nuclei ,$A=238-24=214$ and atomic number,$Z=92-12+8=88.$ So final nuclei should be $\begin{array}{c}214\\ 88\end{array}X$. so statement 2 is false.
Torque ,$\tau =\frac{dL}{dt}$ where L is the angular momentum.
If L is constant then torque is zero. so torque should be perpendicular to L. so statement 3 is true.