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Class 12 › Physics › Moving Charges and Magnetism
CBSE2023Class Class 12 · Physics5 Marks · Long✅ Verified
Two identical charged particles P and Q, each of mass $4 \times 10^{-26}$ kg and charge $4.8 \times 10^{-19}$ C, move with speed $2.4 \times 10^5$ m/s. They are equidistant (0.5 m) from the Y-axis. A magnetic field $B$ is switched on so that the two particles undergo head-on collision. Find: (I) the direction of $B$, and (II) the magnitude of $B$.
✅ Answer & Solution
(I) Direction of $B$:
For head-on collision, the positively charged particles must curve towards each other. Using the right-hand rule with velocity directed towards the Y-axis and force directed inward, $\vec{B}$ must be directed into the page (along $-z$ direction).
(II) Magnitude of $B$:
For head-on collision, each particle must travel a semicircle of radius equal to the initial distance from Y-axis $= 0.5$ m.
$$r = \frac{mv}{qB} \Rightarrow B = \frac{mv}{qr}$$
$$B = \frac{4 \times 10^{-26} \times 2.4 \times 10^5}{4.8 \times 10^{-19} \times 0.5}$$
$$B = \frac{9.6 \times 10^{-21}}{2.4 \times 10^{-19}} = 0.04 \text{ T}$$
