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CBSE Class 12 Physics 2014 Delhi Set 1 Paper

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Question : 10
Total: 30
Give a uniform electric field
→
E
=5×103
^
i
 N/C find the flux of this field through a square of 10‌cm on a side whose plane is parallel to the YZ plane. What would be the flux through the same square if the plane makes a 30∘ angle with the X-axis?
Solution:  
(a) The plane of the square is parallel to the y−z plane. Hence, angle between the unit vector normal to the plane and electric field, θ=0∘
Flux ( Φ) through the plane is given by the relation,
Φ‌=|
→
E
|A‌cos‌θ
‌=5×103×0.01×cos‌0∘
‌=50Nm2∕C
(b) Plane makes an angle of 30∘ with the x-axis. Hence, angle between the unit vector normal to the plane and electric field, θ=60∘
Flux, Φ‌=|
→
E
|A‌cos‌θ
‌=5×103×0.01×cos‌60∘
‌=25Nm2∕C
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