Question

If E and H represents the intensity of electric field and magnetising field respectively, then the unit of E/H will be :

• A. mho
• B. ohm
• C. joule
• D. newton

Hint:

This ratio E/H is known as the wave impedance. Remembering that the impedance of free space is approximately 377 \(\Omega\) can help you instantly recall that the unit must be ohm.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the unit of the ratio of the intensity of the electric field (E) to the intensity of the magnetizing field (H).
Step 2: Key Formula or Approach:
We need to find the SI units for E and H and then determine the unit of their ratio.
Unit of Electric Field (E) is Volts per meter (V/m).
Unit of Magnetizing Field (H) is Amperes per meter (A/m).
Step 3: Detailed Explanation:
The unit of the ratio E/H can be found by dividing their respective SI units.
\[ \text{Unit of } \frac{E}{H} = \frac{\text{Unit of E}}{\text{Unit of H}} = \frac{V/m}{A/m} \] The 'per meter' (m) in the numerator and denominator cancels out.
\[ \text{Unit of } \frac{E}{H} = \frac{V}{A} \] According to Ohm's Law (\(V=IR\)), the ratio of voltage (V) to current (I, in Amperes) is resistance (R).
\[ R (\text{in Ohms, } \Omega) = \frac{V (\text{in Volts})}{I (\text{in Amperes})} \] Therefore, the unit of V/A is the ohm (\(\Omega\)).
Alternatively, for an electromagnetic wave propagating in a medium, the ratio E/H is the impedance of the medium (\(Z\)). For free space, \(E/H = Z_0 = \sqrt{\mu_0/\epsilon_0} \approx 377 \, \Omega\). The unit of impedance is the ohm.
Step 4: Final Answer:
The unit of E/H is the ohm.