Practice Start Test

Electromagnetic Waves

NEET Physics · 97 questions · Page 4 of 10 · Click an option or "Show Solution" to reveal answer

Q31
We consider the radiation emitted by the human body. Which one of the following statements is true?
A The radiation emitted is in the infra-red region
B The radiation emitted only during the day
C The radiation is emitted during the summers and absorbed during the winters
D The radiation emitted lies in the ultraviolet region and hence is not visible
Correct Answer
Option A
Solution

Every body at all time, at all temperatures emit radiation (except at T = 0), which fall in the infrared region.

Q32
What is the cause of Green house effect ?
A infra-red rays
B ultra violet rays
C X-rays
D radio waves.
Correct Answer
Option A
Solution

Infrared ray is the cause of Green House effect.

The glass transmits visible light while infrared rays are absorbed by plants.

Then it emits long infrared rays, which are reflected back by glass.

Q33
The velocity of electromagnetic wave is parallel to
A B→×E→\overrightarrow B \times \overrightarrow E
B E→×B→\overrightarrow E \times \overrightarrow B
C E→\overrightarrow E
D B→\overrightarrow B
Correct Answer
Option B
Solution

Since, the direction of propagation of electromagnetic waves is perpendicular to Electric field and Magnetic field.

Also electric and magnetic fields perpendicular so, direction of the wave will be parallel to

E→×B→\overrightarrow E \times \overrightarrow B

.

Q34
Biological inportance of ozone layer is
A it stops ultraviolet rays
B ozone layer reduces green house effect
C ozone layer reflects radio waves
D ozone layer controls O 2 /H 2 ratio in atmosphertte.
Correct Answer
Option A
Solution

The ozone layer absorbs the harmful ultraviolet rays coming from sun.

Q35
The frequency order for γ\gamma -rays (a), X-rays (b), UV rays (c) is
A b >> a >> c
B a >> b >> c
C c >> b >> a
D a >> c >> b
Correct Answer
Option B
Solution

The frequency of radiations of waves are :

Q36
Light is incident normally on a completely absorbing surface with an energy flux of 25 W cm–2. If the surface has an area of 25 cm2, the momentum transferred to the surface in 40 min time duration will be :
A 6.3 × 10–4 Ns
B 5.0 × 10–3 Ns
C 1.4 × 10–6 Ns
D 3.5 × 10–6 Ns
Correct Answer
Option B
Solution
P=ΔECP = {{\Delta E} \over C}
=(25×25)×40×603×108N−s= {{\left( {25 \times 25} \right) \times 40 \times 60} \over {3 \times {{10}^8}}}N - s
=5×10−2N−s= 5 \times {10^{ - 2}}N - s
Q37
Choose the correct option relating wave lengths of different parts of electromagnetic wave spectrum:
A λ\lambda radio waves > λ\lambda micro waves > λ\lambda visible > λ\lambda x-rays
B λ\lambda visible > λ\lambda x-rays > λ\lambda radio waves > λ\lambda micro waves
C λ\lambda visible < λ\lambda micro waves < λ\lambda radio waves < λ\lambda x-rays
D λ\lambda x-rays < λ\lambda micro waves < λ\lambda radio waves < λ\lambda visible
Correct Answer
Option A
Solution

Decreasing order of wavelength, Radio wave > Microwave > Infrared > ROYGBIV(Visiable Resion) > Ultraviolet > X rays > γ\gamma rays So the correct order - λ\lambdaradio waves > λ\lambdamicro waves > λ\lambdavisible > λ\lambdax-rays

Q38
A plane electromagnetic wave propagating along y-direction can have the following pair of electric field (E→)\left( {\overrightarrow E } \right) and magnetic field (B→)\left( {\overrightarrow B } \right) components.
A Ex, Bz or Ez, Bx
B Ex, By or Ey, Bx
C Ey, By or Ez, Bz
D Ey, Bx or Ex, By
Correct Answer
Option A
Solution

∵\because

E^×B^=C^\widehat E \times \widehat B = \widehat C

∴\therefore

E^×B^\widehat E \times \widehat B

should point in the direction of propagation of wave (y-direction here) ∴\therefore possible combinations are (Ex, Bz) or (Ez, Bx)

Q39
In an electromagnetic wave the electric field vector and magnetic field vector are given as E→=E0i^\overrightarrow E = {E_0}\widehat i and B→=B0k^\overrightarrow B = {B_0}\widehat k respectively. The direction of propagation of electromagnetic wave is along :
A (k^)\left( {\widehat k} \right)
B j^\widehat j
C (−k^)\left( { - \widehat k} \right)
D (−j^)\left( { - \widehat j} \right)
Correct Answer
Option D
Solution

Direction of propagation =

E→×B→=i^×k^=−j^\overrightarrow E \times \overrightarrow B = \widehat i \times \widehat k = - \widehat j
Q40
Sun light falls normally on a surface of area 36 cm236 \mathrm{~cm}^{2} and exerts an average force of 7.2×10−9 N7.2 \times 10^{-9} \mathrm{~N} within a time period of 20 minutes. Considering a case of complete absorption, the energy flux of incident light is
A 25.92×102 W/cm225.92 \times 10^{2} \mathrm{~W} / \mathrm{cm}^{2}
B 8.64×10−6 W/cm28.64 \times 10^{-6} \mathrm{~W} / \mathrm{cm}^{2}
C 6.0 W/cm26.0 \mathrm{~W} / \mathrm{cm}^{2}
D 0.06 W/cm20.06\mathrm{~W} / \mathrm{cm}^{2}
Correct Answer
Option D
Solution

Pressure

=lc= {l \over c}
⇒FA=lc\Rightarrow {F \over A} = {l \over c}
⇒l=7.2×10−9×3×10836×10−4\Rightarrow l = {{7.2 \times {{10}^{ - 9}} \times 3 \times {{10}^8}} \over {36 \times {{10}^{ - 4}}}}

W/m2

=600= 600

W/m2

⇒l=0.06\Rightarrow l = 0.06

W/cm2

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