Solutions of Electromagnetic Waves Test 01 - Class 12

 Page 1


CBSE TEST PAPER-01 
CLASS - XII PHYSICS (Electro magnetic waves) 
[ANSWERS] 
Ans 1: It absorbs all the harmful ultraviolet radiations thus protecting us from reaching the 
dangerous effects of uv radiations. 
Ans 2: Microwaves are used in Radar. 
Ans 3: (1) infra-red radiations are used to take photographs under foggy conditions. 
(2) Infra-red radiations are used in revealing the secret writings on the ancient 
walls. 
Ans 4: (1) X -Rays 
(2) Microwaves 
Ans 5: (a) 
O
O
E
C
B
=
O
O
E
B
C
=
8
60
3 10
=
×
Since magnetic field and electric field are ? to each other
? By = 2 × 10
-7
 T sin 
( )
3
11
10 3
10
2 2
t
x
? ?
+
? ?
? ?
---------------- (1) 
 Compare e.g. (1) with standard equation 
 By = B O sin 2
x t
T
p
?
? ?
+
? ?
? ?
( )
11
11
1 3
 2 10
2
1 3 10
2 2
Also
T
T
p
?
p
=
×
= =
×
Ans 6: (a) V = 2 × 10
10
 Hz
 E O = 48 V/m 
8
10
3 10
2 10
C
V
?
×
= =
×
B
O
 = 2 ×10
-7
 T 
3
4 10 m ? p
- = ×
11
3
10
4
Hz ?
p
= ×
2
1.5 10 m ?
- = × 
Page 2


CBSE TEST PAPER-01 
CLASS - XII PHYSICS (Electro magnetic waves) 
[ANSWERS] 
Ans 1: It absorbs all the harmful ultraviolet radiations thus protecting us from reaching the 
dangerous effects of uv radiations. 
Ans 2: Microwaves are used in Radar. 
Ans 3: (1) infra-red radiations are used to take photographs under foggy conditions. 
(2) Infra-red radiations are used in revealing the secret writings on the ancient 
walls. 
Ans 4: (1) X -Rays 
(2) Microwaves 
Ans 5: (a) 
O
O
E
C
B
=
O
O
E
B
C
=
8
60
3 10
=
×
Since magnetic field and electric field are ? to each other
? By = 2 × 10
-7
 T sin 
( )
3
11
10 3
10
2 2
t
x
? ?
+
? ?
? ?
---------------- (1) 
 Compare e.g. (1) with standard equation 
 By = B O sin 2
x t
T
p
?
? ?
+
? ?
? ?
( )
11
11
1 3
 2 10
2
1 3 10
2 2
Also
T
T
p
?
p
=
×
= =
×
Ans 6: (a) V = 2 × 10
10
 Hz
 E O = 48 V/m 
8
10
3 10
2 10
C
V
?
×
= =
×
B
O
 = 2 ×10
-7
 T 
3
4 10 m ? p
- = ×
11
3
10
4
Hz ?
p
= ×
2
1.5 10 m ?
- = × 
(b) E O = cB O 
8
48
3 10
O
O
E
B
C
= =
×
(c) Energy density 
2
1
2
O
U E = ?
12
1
8.85 10 48 48
2
U
- = × × × 
Ans 7: V = 6 × 10
12
 Hz
8
12
Using 
3 10
6 10
c
v
?
?
=
×
=
×
These are infra-red radiations 
Applications  
(1) It keeps the earth warm.  
(2) Infra-red lamps are used to treat muscular strains. 
Ans 8: (a) The direction of propagation of wave is along + x – axis. 
(b) Amplitude = 4 units 
(c) Component of magnetic of field 
8
4
3 10
Eo
Bz
C
= =
×
Ans 9: Characteristics of em waves 
(1) It travels in free space with speed of light c = 3 x 10
8
 m/s. 
(2) Electromagnetic waves are transverse in nature.  
Velocity of em waves in vacuum C = 
1
o o
µ ?
8
16 10 Tesla
O
B
- = ×
U = 1 ×10
-8
 J/m
3
 
5
5 10 m ?
- = × 
Bz = 1.33 ×10
-8
 Tesla