Question 18
Before a thunderstorm,
the hairs on your head sometimes stand on end.
A hair with mass 0.50
mg and charge 1.0 pC is supported by a force due to an electric field.
Ignore any forces
other than the weight of the hair and the electric force.
What is the electric
field strength?
A 4.9
× 103 N C-1
B 4.9
× 105 N C-1
C 4.9
× 106 N C-1
D 4.9
× 109 N C-1
Reference: Past Exam Paper – June 2016 Paper 12 Q30
Solution:
Answer:
C.
The electric force is
equal to the weight.
Electric force = Weight
Eq = mg
Electric field strength E
= mg / q
{mass should be in kg.}
E = (0.5×10-6) ×
9.81 / (1.0×10-12)
E = 4.9×106 N C-1
the answer is D why did you put C
ReplyDeletethere was a mistake. it has been corrected.
Deletethe answer is C.
why did we multiply 0.5 with 10^-6?
ReplyDeleteto convert mg to kg
DeleteI'm still wondering: how is the electric force equal to the weight?
ReplyDeleteThe fact that the hair stands means that the forces are equal. If the weight was greater, the hair would have moved down and if the electric force was greater, the hair would have moved up.
Delete