direct currents and alternating currents .pptx

Direct and alternating current IGCSE

1. Direct and alternating currents © Pearson Education Ltd 2019. Copying permitted for purchasing institutions only. This material is not copyright free.

2. Energy is transferred from cells and batteries to the components in a circuit when charge passes through them. © Pearson Education Ltd 2019. Copying permitted for purchasing institutions only. This material is not copyright free. Electrons are ‘pushed’ away from the negative terminal of the cell. Electrons transfer energy to components as they flow through them. Electrons returning to the cell have less energy than the electrons leaving the cell.

3. Cells and batteries provide a direct voltage . The direction of the potential difference they provide stays the same. © Pearson Education Ltd 2019. Copying permitted for purchasing institutions only. This material is not copyright free. Electrons are ‘pushed’ away from the negative terminal of the cell. Electrons always flow around the circuit in the same direction. Electrons return to the positive terminal.

4. In any circuit, the current is always in the same direction as the potential difference. If you remove a cell and put it back the other way, the current will be in the opposite direction. © Pearson Education Ltd 2019. Copying permitted for purchasing institutions only. This material is not copyright free. The direction of the potential difference from a cell does not change, so the current is constant. The blue line shows the current when a cell is replaced by a lower voltage cell put into the circuit the other way round.

5. If you could instantaneously keep swapping the direction of the cell, the current would keep changing direction. © Pearson Education Ltd 2019. Copying permitted for purchasing institutions only. This material is not copyright free. This is a form of alternating current , as the direction of the current is in one direction and then the other.

6. Power stations produce electricity using rotating generators. The direction of the potential difference changes many times each second. A graph of the alternating current ( a.c .) produced by a power station looks like this: © Pearson Education Ltd 2019. Copying permitted for purchasing institutions only. This material is not copyright free. In the UK the alternating current from the mains supply has a frequency of 50 Hz. This means that each complete cycle takes s, or 0.02 s.   0.02 s

7. In the UK the alternating current from the mains supply has a frequency of 50 hertz (50 Hz). This means that it changes direction 100 times each second (every 0.01 s), so a complete cycle takes 0.02 s. © Pearson Education Ltd 2019. Copying permitted for purchasing institutions only. This material is not copyright free. 0.01 s 0.01 s 0.02 s

8. Explain whether each of these graphs is showing alternating or direct current. © Pearson Education Ltd 2019. Copying permitted for purchasing institutions only. This material is not copyright free.

9. © Pearson Education Ltd 2019. Copying permitted for purchasing institutions only. This material is not copyright free. This is direct current. Although the size of the current varies, it is always in a positive direction. This is alternating current. The current is mostly in the positive direction, but does go in the negative direction some of the time.

10. © Pearson Education Ltd 2019. Copying permitted for purchasing institutions only. This material is not copyright free. This is direct current. It is in the negative direction all the time, so its direction does not change. This is alternating current. The direction of the current changes regularly.