Answer:
A) equal to the battery's terminal voltage.
Explanation:
When the capacitor is fully charged after long hours of charging , its potential becomes equal to the emf of the battery and its polarity is opposite to that of battery . Hence net emf becomes equal . The capacitor itself becomes a battery which is connected in the circuit with opposite polarity . This results in the net emf and current becoming zero . There is no charging current when the capacitor is fully charged .
The best answer is B)
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Answer with Explanation:
We are given that
Resistance of solenoid,R=4.3 ohm
Magnetic field,B=
Current,I=4.6 A
Diameter of wire,d=0.5 mm=
Radius of wire,r=

Radius of solenoid,r'=1 cm=

Resistivity of copper,
We know that

Where 
Using the formula


Number of turns of wire=
Number of turns of wire=
Hence, the number of turns of the solenoid,N=799
Magnetic field in solenoid,B=






Length of solenoid=12.5 cm
1m=100 cm
Using the given equation:
di = 20.0 * 10.0 / 20.0 - 10.0
di = 200/10
di = 20.0 cm
The answer is A.