Electric Current (CIE A Level Physics)

The smallest conductor within a computer processing chip can be represented as a rectangular block that is one atom high, four atoms wide and twenty atoms long. One such block is shown in Fig. 1.1.

Fig. 1.1.

The block is made from phosphorus atoms of diameter d = 3.8 × 10^–10 m. The atoms are deposited on an insulating surface. This ensures that the atoms touch each other.

The processing chip has a resistance, measured from P to Q, of 220 Ω.

Calculate the number density of free electrons within the block.

Assume that each phosphorus atom contributes one free electron.

Calculate the current between P and Q when the mean drift velocity of free electrons in the block is 1.9 × 10^–5 ms^–1.

There are about 10⁹ of these tiny conductors in a single chip each carrying the current calculated in part (c).

Estimate the total power dissipated in these conductors in a single chip.

A power source is connected across a component. The current in the component is 40 mA.

Calculate the total charge that flows past a point in the component in 3 minutes.

Calculate the number of electron charge carriers passing the same point in the conductor in this time.

8.6 J of energy are transferred to the conductor in this time.      

Nancy is testing a new type of light bulb. She records the amount of current and the relative brightness of the light coming from the bulb. 

Sketch a possible circuit diagram to show this experimental setup. 

Explain why the ammeter needs to be connected in series.

Explain the results Nancy should expect to obtain, assuming the resistance of the bulb, ammeter and circuit remain constant.

Nancy sets up her circuit and begins to conduct her experiment. Her first readings are negative values of current. 

Identify the problem and suggest a solution.