Name a device that help to maintain a potential difference across a conductor?

Name a device used to measure potential difference between two points in a circuit?

How does the mobility of electrons in a conductor change, if the potential difference applied across the conductor is doubled keeping the length and temperature of the conductor constant.

A capacitor of capacity 100 muF is charged to a potential difference of 12 V. It is then connected across an inductor of inductance 6 mu H . What is the current (in A) in the circuit at a time when the potential difference across the capacitor is 6.0 V?

Length of a conductor is increased to three times. What is the effect on resistance if potential across the conductor is kept constant.

A charge of 2 C moves between two plates maintained at a potential difference of 1 volt. What is the energy acquired by the charge?

Derive the expression for the heat produced due to a current 'I' flowing for a time interval 't' through a resistor 'R' having a potential difference 'V' across its ends. With which name is this relation known ?