electromagnetic-waves Question 29
Question: Q. 1. Compare the following:
(i) Wavelengths of the incident solar radiation absorbed by the earth’s surface and the radiation re-radiated by the earth. (ii) Tanning effect produced on the skin by UV radiation incident directly on the skin and that coming through glass window.
U] [CBSE SQP 2018-19]
Show Answer
Solution:
Ans. (i) Radiation re-radiated by earth has greater wavelength
(ii) Tanning effect is significant for direct UV radiation; it is negligible for radiation coming through the glass.
[CBSE Marking Scheme, 2018]
[AI Q. 2. Identify the electromagnetic waves whose wavelengths vary as :
(i) $10^{-12} \mathrm{~m}<\lambda<10^{-8} \mathrm{~m}$
(ii) $10^{-3} \mathrm{~m}<\lambda<10^{-1} \mathrm{~m}$
Write one use for each.
U] [O.D. I 2017]
| Ans. (i) Identification | $1 / 2+1 / 2$ |
|---|---|
| (ii) Uses | $1 / 2+1 / 2$ |
| (i) $X$-rays | $1 / 2$ |
| Used for medical purposes. | $1 / 2$ |
| (Also accept UV rays and gamma rays and any | |
| one use of the EM wave named) |
(ii) Microwaves
Used in radar systems.
(Also accept short radio waves and any one use of the EM wave named)
[CBSE Marking Scheme 2017]
Detailed Answer :
(i) Wavelength $10^{-12} \mathrm{~m}<\lambda<10^{-8} \mathrm{~m}$ shows the existence of $X$-rays
$X$ - radiation takes place due to electron transition among upper and lower energy levels of heav elements that are excited by electron bombardment. $X$-rays are mainly used in medicine and dentistry which can be detected using photographic film. 1
(ii) Wavelength $10^{-3} \mathrm{~m}<\lambda<10^{-1} \mathrm{~m}$ shows the existence of Microwaves.
Microwaves are produced by magnetron which are used in radar, telemetry and electron spin resonance studies and in microwave ovens. Microwaves are detected with crystal detectors or solid-state diodes. $\mathbf{1}$
