Assertion (A): A magnetic needle when placed in between the plates of a parallel plate capacitor under charging, the needle shows deflection.
Reason (R):As the charge on the capacitor plates increases, the electric field and the electric flux between the plates changes which generates a magnetic field.
1. Both (A) &(R) are true and the (R) is the correct explanation of the (A)
2. Both (A) &(R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
During capacitor charging, the changing electric field produces a displacement current \(I_d = epsilon_0 frac{dPhi_E}{dt}\). This displacement current generates a magnetic field, causing the needle to deflect. Thus, A and R are true, and R explains A.
Assertion (A): In an electromagnetic wave, magnitude of magnetic field vector is much smaller than the magnitude of electric field vector.
Reason (R): Energy of electromagnetic waves is shared equally by the electric and magnetic fields.
1. Both (A) &(R) are true and the (R) is the correct explanation of the (A)
2. Both (A) &(R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
In an EM wave, \(E_0 = cB_0\). Since \(c = 3 times 10^8 text{ m/s}\), \(E_0\) is much larger than \(B_0\) in SI units, so A is true. Energy is equally shared between fields, so R is true. However, R does not explain why \(E_0\) is numerically larger than \(B_0\).
**Assertion (A):** The gyrating electron can be a source of EMW.
**Reason (R):** The electron in circular motion is accelerated motion.
1. Both (A) &(R) are true and the (R) is the correct explanation of the (A)
2. Both (A) &(R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer
A gyrating electron undergoes circular motion, which is accelerated motion. Accelerated charges are sources of electromagnetic waves. Therefore, Assertion and Reason are true, and R correctly explains A.