Current electricity
1.

A conductor carries a current of 0.4 A. Find the amount of charge that will pass through the cross – section of the conductor in 42 s. How many electrons will flow in this time interval if charge on one electron is 1.6 × 10 – 19C ?

Sol:
Given, I = 0.4 A, t = 42 s
Charge = Current × time
Q = I × t
= 0.4 × 42
= 16.8C

If n electrons flow and e is the charge on one electron, then total charge passed Q = ne

∴ n = Q/e
= 16.8/(1.6 × 10 – 19)
= 10.5 × 1019.
2.

You are given a conducting wire connected with a cell and a key. You are required to measure the current in the wire and potential difference across it. Name the instruments that you would use and draw a labelled diagram to show how are they connected. Also mark the direction of current in each component ?

Sol:

To measure current, an ammeter is used and to measure the potential difference a voltmeter is required.
The ammeter (A) is connected in series with the wire and the cell while the voltmeter (V) is connected in parallel across the wire.
The complete diagram is given in figure.
The arrow marked in the diagram shows the direction of current.