Question

Identify the correct statements among the following.
A. All electromagnetic waves, irrespective of their frequencies, travel at the same speed through vacuum.
B. A capacitor is fully charged by a d.c. source. When it is fully charged, the displacement current is zero.
C. Ultraviolet radiation can be used for viewing objects through haze and fog.
D. A moving charge in a circular orbit cannot produce electromagnetic waves.
Choose the correct answer from the options given below:

• A. A, B and C only
• B. B and C only
• C. A and B only
• D. C and D only

Hint:

Infrared, not UV, penetrates haze. Accelerated charges radiate.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Each statement tests a basic idea about electromagnetic waves. Check them one by one.

Step 2: Check statement (A):
In vacuum every electromagnetic wave travels at \(c = 1/\sqrt{\mu_0\varepsilon_0} \approx 3\times10^8\) m/s, whatever its frequency. So (A) is TRUE.

Step 3: Check statement (B):
Once a capacitor is fully charged by a d.c. source, the electric field between the plates stops changing. Then \(d\Phi_E/dt = 0\), so the displacement current is zero. So (B) is TRUE.

Step 4: Check statement (C):
Haze and fog particles scatter short wavelengths strongly. UV scatters far more than infrared, so it cannot pass through. Infrared is used to see through haze and fog. So (C) is FALSE.

Step 5: Check statement (D):
A charge moving in a circle is accelerating, because its velocity direction keeps changing. An accelerated charge radiates electromagnetic waves. So (D) is FALSE.

Step 6: Pick the option:
Only A and B are correct, which is option 3.

Final Answer:
Statements A and B are correct. \[ \boxed{A \text{ and } B \text{ only}} \]