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An electromagnetic wave of frequency u = 3.0 MHz passes from vacuum into a dielectric medium with permitivity ε = 4.0. Then

Asked in JEE Main 2004 · Crossing an interface

• (1) wavelength is doubled and the frequency remains unchanged
• (2) wavelength is doubled and frequency becomes half
• (3) wavelength is halved and frequency remains unchanged
• (4) wavelength and frequency both remain unchanged.

Step-by-step solution

Why the other options are wrong

• (1) comes from a doubled wavelength needs a doubled speed; a dielectric slows the wave
• (2) comes from frequency is fixed by the source — it never changes on crossing a boundary
• (4) comes from with u fixed and v = c/2, λ = v/ u must fall

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