Question

Assertion : $\beta -particles$ are deflected more than $\alpha -particles$ in a given electric field.
Reason : Charge on $\alpha -particles$ is larger than on $\beta -particles$.

• A. If both (A) and (R) are correct, and (R) is the correct explanation of (A).
• B. If both (A) and (R) are correct, but (R) is not the correct explanation of (A).
• C. If (A) is correct, but (R) is incorrect.
• D. If (A) is incorrect, but (R) is correct.
• E. If both (A) and (R) are incorrect.

Answer 1

Answer: (B)

If both (A) and (R) are correct, but (R) is not the correct explanation of (A).

The Alpha particle is a helium nucleus; it consists of two protons and two neutrons. It contains no electrons to balance the two positively charged protons. Alpha particles are therefore positively charged particles moving at high speeds. Alpha particles are attracted to the negatively charged plate.

Beta particles are high energy electrons. Beta particles are negatively charged. Beta particles are fast-moving electrons with a very low mass and so have a high charge to mass density. They are deflected much more than the heavier alpha particles due to this charge to mass density.