Current and Charge

A copper wire carries a constant current of 2.5 A. Which statement is correct?

• The number of electrons passing a point in the wire each second is constant.

• The charge passing a point in the wire each second is constant.

• The potential difference across the wire is constant.

• The drift velocity of the electrons is constant.

A battery is connected to a calculator, transferring a total charge of 360 C over a period of 5.0 minutes. (a) Calculate the average current supplied to the calculator.

The calculator operates at a constant current of 1.2 A. How many electrons flow through it in 10 seconds? (Elementary charge e = 1.60 × 10⁻¹⁹ C)

Two copper wires, X and Y, are of equal length. Wire X has twice the cross-sectional area of wire Y. The same current flows through both wires. Which comparison of drift velocity v and number density n is correct?

• same 2 × v_Y

• same ½ × v_Y

• 2 × n_Y same

• ½ × n_Y same

A steady current I flows in a wire of cross-sectional area A. The charge carriers are electrons, each with charge e. (a) State what is represented by the symbol n in the equation I = Anvq.

The number density of free electrons in copper is 8.5 × 10²⁸ m⁻³. A copper wire of diameter 1.2 mm carries a current of 3.5 A. Calculate the mean drift velocity of the electrons.

Which of the following is a correct unit for the quantity (charge / time)?

• Joule (J)

• Watt (W)

• Ampere (A)

• Volt (V)

A beam of alpha particles consists of 2.0 × 10⁶ particles per second. Each alpha particle has a charge of +3.2 × 10⁻¹⁹ C. Calculate the beam current.

A metal wire is stretched to twice its original length without a change in volume. What happens to the number density *n* of free electrons and the drift velocity *v* of the electrons when the same current flows? Assume the material's resistivity remains constant.

• halves unchanged

• halves doubles

• unchanged halves

• unchanged quadruples