Electromagnetic Waves - Result Question 7
7. An electromagnetic wave of frequency $v=3.0$ $MHz$ passes from vacuum into a dielectric medium with relative permittivity $\varepsilon=4.0$. Then
[NEET Kar. 2013]
(a) wavelength is doubled and frequency is unchanged
(b) wavelength is doubled and frequency becomes half
(c) wavelength is halved and frequency remains unchanged
(d) wavelength and frequency both remain unchanged
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Answer:
Correct Answer: 7. (c)
Solution:
- (c) Given: frequency $f=2 MHz$, relative permittivity $\epsilon_r=4$
From formula,
velocity $v=\frac{c}{\sqrt{\epsilon_r}}=\frac{c}{2} \Rightarrow \lambda^{\prime}=\frac{\lambda}{2}$
[Since frequency remains unchanged]
