Question

Among the following, the electromagnetic wave of minimum frequency is:

• A. ultraviolet rays
• B. X-rays
• C. \( \gamma \)-rays
• D. microwaves

Hint:

Order the spectrum by frequency; the wave with the longest wavelength (using \( \nu = c/\lambda \)) has the least frequency.

Answer 1

The Correct Option is D

Step 1: Recall the electromagnetic spectrum order.
Arranged in order of increasing frequency (and therefore decreasing wavelength), the electromagnetic spectrum runs as:
radio waves < microwaves < infrared < visible light < ultraviolet < X-rays < \( \gamma \)-rays.

Step 2: Place the four given waves in this order.
From lowest to highest frequency among the options:
microwaves < ultraviolet rays < X-rays < \( \gamma \)-rays.

Step 3: Pick the minimum frequency.
Microwaves lie farthest toward the low-frequency (long-wavelength) end of these four, so they have the smallest frequency.

Step 4: Choose the correct option.
Hence the electromagnetic wave of minimum frequency is microwaves, option (iv). \( \gamma \)-rays actually have the highest frequency, and X-rays and ultraviolet rays are also higher in frequency than microwaves.

\[\boxed{\text{Microwaves have the minimum frequency}}\]