Electromagnetic Waves Practice Questions - DPP for JEE

 Page 1


1. (b) Q The E.M. wave are transverse in nature i.e.,
= …(i)
where 
and … (ii)
 is ?  and  is also ? to 
or    In other words  and 
2. (d) The direction of propagation of electromagnetic wave is
perpendicular to both electric field E and magnetic field B, i.e., in
the direction of E × B by right thumb rule.
The diagram given below
So, electromagnetic wave is along the z-direction which is give the cross
product of E and B direction is perpendicular to E and B from 
. i.e., (E × B) in z-direction.
3. (a) Direction of energy progration of EM-waves is given by
 =  or  = 
Clearly direction of magnetic field is along positive x-axis.
4. (b) EM waves carry momentum and hence can exert pressure on
surfaces. They also transfer energy to the surface so p ? 0 and E ?
0.
Page 2


1. (b) Q The E.M. wave are transverse in nature i.e.,
= …(i)
where 
and … (ii)
 is ?  and  is also ? to 
or    In other words  and 
2. (d) The direction of propagation of electromagnetic wave is
perpendicular to both electric field E and magnetic field B, i.e., in
the direction of E × B by right thumb rule.
The diagram given below
So, electromagnetic wave is along the z-direction which is give the cross
product of E and B direction is perpendicular to E and B from 
. i.e., (E × B) in z-direction.
3. (a) Direction of energy progration of EM-waves is given by
 =  or  = 
Clearly direction of magnetic field is along positive x-axis.
4. (b) EM waves carry momentum and hence can exert pressure on
surfaces. They also transfer energy to the surface so p ? 0 and E ?
0.
5. (b) Here, k = , ? = 2p?
? ( Q c = ? ?)
where c is the speed of electromagnetic wave in vacuum. It is a
constant whose value is 3 × 10
6
 ms
–1
6. (c) = 
or  = ? 
7. (b) Comparing with the equation of wave.
E
y
 = E
0
  cos (?t – kx)
? = 2 pf = 2p × 10
6          
?   f = 10
6
 Hz
= k = p × 10
–2
 m
–1
, ? = 200 m
8. (c) Speed of EM waves in vacuum 
9. (d) is electric energy density.
 is magnetic energy density.
So, total energy = 
10. (c) Gamma rays < X-rays < Ultra violet < Visible rays < Infrared rays
< Microwaves < Radio waves.
11. (d) To generate electromagnetic waves we need accelerating charge
particle.
12. (c) Pressure = I/c
13. (b) Audible waves are not electromagnetic wave.
14. (b) All components of electromagnetic spectrum travel in vacuum
Page 3


1. (b) Q The E.M. wave are transverse in nature i.e.,
= …(i)
where 
and … (ii)
 is ?  and  is also ? to 
or    In other words  and 
2. (d) The direction of propagation of electromagnetic wave is
perpendicular to both electric field E and magnetic field B, i.e., in
the direction of E × B by right thumb rule.
The diagram given below
So, electromagnetic wave is along the z-direction which is give the cross
product of E and B direction is perpendicular to E and B from 
. i.e., (E × B) in z-direction.
3. (a) Direction of energy progration of EM-waves is given by
 =  or  = 
Clearly direction of magnetic field is along positive x-axis.
4. (b) EM waves carry momentum and hence can exert pressure on
surfaces. They also transfer energy to the surface so p ? 0 and E ?
0.
5. (b) Here, k = , ? = 2p?
? ( Q c = ? ?)
where c is the speed of electromagnetic wave in vacuum. It is a
constant whose value is 3 × 10
6
 ms
–1
6. (c) = 
or  = ? 
7. (b) Comparing with the equation of wave.
E
y
 = E
0
  cos (?t – kx)
? = 2 pf = 2p × 10
6          
?   f = 10
6
 Hz
= k = p × 10
–2
 m
–1
, ? = 200 m
8. (c) Speed of EM waves in vacuum 
9. (d) is electric energy density.
 is magnetic energy density.
So, total energy = 
10. (c) Gamma rays < X-rays < Ultra violet < Visible rays < Infrared rays
< Microwaves < Radio waves.
11. (d) To generate electromagnetic waves we need accelerating charge
particle.
12. (c) Pressure = I/c
13. (b) Audible waves are not electromagnetic wave.
14. (b) All components of electromagnetic spectrum travel in vacuum
with velocity 3 × 10
8
 m/s.
15. (c) Electromagnetic waves are the combination of mutually
perpendicular electric and magnetic fields.
16. (a) Momentum of light falling on reflecting surface p = 
As surface is perfectly reflecting so momentum reflect p
1
 = – 
So, momentum transferred
= P – P
1
 =  = 
17. (d)
18. (a) . also  and 
These relation gives E
0
k = B
0
?
19. (c) Speed of light of vacuum  and in another medium 
? .
20. (d) Wave is UV rays.
21. (100)
22. (5.8)
23. (3.1 × 10
–8
)
Velocity of light
Page 4


1. (b) Q The E.M. wave are transverse in nature i.e.,
= …(i)
where 
and … (ii)
 is ?  and  is also ? to 
or    In other words  and 
2. (d) The direction of propagation of electromagnetic wave is
perpendicular to both electric field E and magnetic field B, i.e., in
the direction of E × B by right thumb rule.
The diagram given below
So, electromagnetic wave is along the z-direction which is give the cross
product of E and B direction is perpendicular to E and B from 
. i.e., (E × B) in z-direction.
3. (a) Direction of energy progration of EM-waves is given by
 =  or  = 
Clearly direction of magnetic field is along positive x-axis.
4. (b) EM waves carry momentum and hence can exert pressure on
surfaces. They also transfer energy to the surface so p ? 0 and E ?
0.
5. (b) Here, k = , ? = 2p?
? ( Q c = ? ?)
where c is the speed of electromagnetic wave in vacuum. It is a
constant whose value is 3 × 10
6
 ms
–1
6. (c) = 
or  = ? 
7. (b) Comparing with the equation of wave.
E
y
 = E
0
  cos (?t – kx)
? = 2 pf = 2p × 10
6          
?   f = 10
6
 Hz
= k = p × 10
–2
 m
–1
, ? = 200 m
8. (c) Speed of EM waves in vacuum 
9. (d) is electric energy density.
 is magnetic energy density.
So, total energy = 
10. (c) Gamma rays < X-rays < Ultra violet < Visible rays < Infrared rays
< Microwaves < Radio waves.
11. (d) To generate electromagnetic waves we need accelerating charge
particle.
12. (c) Pressure = I/c
13. (b) Audible waves are not electromagnetic wave.
14. (b) All components of electromagnetic spectrum travel in vacuum
with velocity 3 × 10
8
 m/s.
15. (c) Electromagnetic waves are the combination of mutually
perpendicular electric and magnetic fields.
16. (a) Momentum of light falling on reflecting surface p = 
As surface is perfectly reflecting so momentum reflect p
1
 = – 
So, momentum transferred
= P – P
1
 =  = 
17. (d)
18. (a) . also  and 
These relation gives E
0
k = B
0
?
19. (c) Speed of light of vacuum  and in another medium 
? .
20. (d) Wave is UV rays.
21. (100)
22. (5.8)
23. (3.1 × 10
–8
)
Velocity of light
24. (4.58 × 10
–6
)
E
rms
 = 720
The average total energy density
 
= 8.85 × 10
–12
 × (720)
2
= 4.58 × 10
–6
 J/m
3
25. (2.68) Wavelength of monochromatic green light
= 5.5 × 10
–5
 cm
Intensity I = 
=   = 
Now, half of this intensity (I) belongs to electric field and half of that to
magnetic field, therefore,
or
=  =  = 
? E
0
 = 2.68 V/m