1. SACE Stage 1 Conceptual Physics Electric Current

2. Flow of Charge Voltage is an electrical pressure that can produce a flow of charge or an electric current within a conductor. Voltage is an electrical pressure that can produce a flow of charge or an electric current within a conductor. The flow is restrained by the resistance it encounters. The flow is restrained by the resistance it encounters.

3. Flow of Charge When the flow takes place in one direction, it is called direct current (dc). When the flow takes place in one direction, it is called direct current (dc). When the flow of charge is to and fro, it is called alternating current (ac). When the flow of charge is to and fro, it is called alternating current (ac).

4. Flow of Charge Heat flows through a conductor when one end is warmer than the other end. Heat flows through a conductor when one end is warmer than the other end. The heat stops flowing when the ends have the same temperature The heat stops flowing when the ends have the same temperature

5. Flow of Charge Similarly, electricity flow in a conductor when the ends have different potential (a potential difference). Similarly, electricity flow in a conductor when the ends have different potential (a potential difference). The electrons will keep flowing until the ends are at the same potential. The electrons will keep flowing until the ends are at the same potential.

6. Flow of Charge To sustain a flow of charge in a conductor, there must be some arrangement where the potential difference can be maintained. To sustain a flow of charge in a conductor, there must be some arrangement where the potential difference can be maintained. This is like maintaining water flow from a higher reservoir to a lower reservoir. This is like maintaining water flow from a higher reservoir to a lower reservoir.

7. Flow of Charge Water flows from the reservoir of high pressure to the reservoir of low pressure until the pressure is equal. The picture on the right shows that water will continue to flow due to the pump which is maintaining the pressure difference. Water flows from the reservoir of high pressure to the reservoir of low pressure until the pressure is equal. The picture on the right shows that water will continue to flow due to the pump which is maintaining the pressure difference.

8. Electric Current The flow of charge in a conductor. The flow of charge in a conductor. In solid conductors it is the electrons that carry the charge through the circuit. In solid conductors it is the electrons that carry the charge through the circuit. This happens because these electrons (conduction electrons) are free to move throughout the atomic network. This happens because these electrons (conduction electrons) are free to move throughout the atomic network.

9. Electric Current Electric Current is measured in amperes (A). Electric Current is measured in amperes (A). An ampere is the flow of one coulomb of charge per second. An ampere is the flow of one coulomb of charge per second. 1 Coulomb = 6.25 billion electrons

10. Voltage Sources Charges do not flow unless there is a potential difference. Charges do not flow unless there is a potential difference. A sustained current needs a suitable “electric pump” to provide a sustained potential difference. A sustained current needs a suitable “electric pump” to provide a sustained potential difference. Something that provides a potential difference is known as a voltage source. Something that provides a potential difference is known as a voltage source.

11. Voltage Sources The potential energy per coulomb of charge available to electrons moving between the terminals is known as the electromotive force or emf. The potential energy per coulomb of charge available to electrons moving between the terminals is known as the electromotive force or emf.

12. Electrical Resistance Similar to the rate of water flow in a hose, the harder the water find it to move through the hose, the less water flows. Similar to the rate of water flow in a hose, the harder the water find it to move through the hose, the less water flows.

13. Electrical Resistance In a wire, a number of factors apply, In a wire, a number of factors apply, Thickness of wire Thickness of wire Type of wire Type of wire Voltage source Voltage source Units of resistance is the ohm (  ). Units of resistance is the ohm (  ).

14. Ohm’s Law Ohm discovered that the amount of current in a circuit is directly proportional to the voltage impressed across the circuit, and is inversely proportional to the resistance of the circuit. Ohm discovered that the amount of current in a circuit is directly proportional to the voltage impressed across the circuit, and is inversely proportional to the resistance of the circuit.

15. Ohm’s Law Q – What is the resistance of an electric frying pan that draws 12 amperes of current when connected to a 120 volt circuit? Q – What is the resistance of an electric frying pan that draws 12 amperes of current when connected to a 120 volt circuit?

16. Ohm’s Law Q – What is the resistance of an electric frying pan that draws 12 amperes of current when connected to a 120 volt circuit? Q – What is the resistance of an electric frying pan that draws 12 amperes of current when connected to a 120 volt circuit? A – The resistance is 10 ohms. (why?) A – The resistance is 10 ohms. (why?)

17. Ohm’s Law Q – What is the resistance of an electric frying pan that draws 12 amperes of current when connected to a 120 volt circuit? Q – What is the resistance of an electric frying pan that draws 12 amperes of current when connected to a 120 volt circuit? A – The resistance is 10 ohms. (why?) A – The resistance is 10 ohms. (why?)

18. Ohm’s Law Q – How much current is drawn by a lamp that has a resistance of 100 ohms when a voltage of 50 volts is impressed across it? Q – How much current is drawn by a lamp that has a resistance of 100 ohms when a voltage of 50 volts is impressed across it?

19. Ohm’s Law Q – How much current is drawn by a lamp that has a resistance of 100 ohms when a voltage of 50 volts is impressed across it? Q – How much current is drawn by a lamp that has a resistance of 100 ohms when a voltage of 50 volts is impressed across it? A – The current is 0.5 ampere. (Why?) A – The current is 0.5 ampere. (Why?)

20. Ohm’s Law Q – How much current is drawn by a lamp that has a resistance of 100 ohms when a voltage of 50 volts is impressed across it? Q – How much current is drawn by a lamp that has a resistance of 100 ohms when a voltage of 50 volts is impressed across it? A – The current is 0.5 ampere. (Why?) A – The current is 0.5 ampere. (Why?)

21. Ohm’s Law and Electric Shock What causes electric shock? What causes electric shock? Current or Voltage

22. Ohm’s Law and Electric Shock Current causes the electric shock. Current causes the electric shock. You can be exposed to a large voltage but if the resistance is very high, not much current will pass through you and you will be safe. You can be exposed to a large voltage but if the resistance is very high, not much current will pass through you and you will be safe.

23. Ohm’s Law and Electric Shock The resistance of your body depends on its condition. The resistance of your body depends on its condition. If your are soaked in salt water you will have a resistance of about 100 ohms. If your are soaked in salt water you will have a resistance of about 100 ohms. If your skin is very dry, about 500,000 ohms. If your skin is very dry, about 500,000 ohms.

24. Ohm’s Law and Electric Shock

25. Q – If the resistance of your body were 100, 000 ohms, how much current would be produced in your body if you touched the terminals of 12V battery? Q – If the resistance of your body were 100, 000 ohms, how much current would be produced in your body if you touched the terminals of 12V battery?

26. Ohm’s Law and Electric Shock Q – If the resistance of your body were 100, 000 ohms, how much current would be produced in your body if you touched the terminals of 12V battery? Q – If the resistance of your body were 100, 000 ohms, how much current would be produced in your body if you touched the terminals of 12V battery? A – The current in your body would be 0.00012 A. (Why ?) A – The current in your body would be 0.00012 A. (Why ?)

27. Ohm’s Law and Electric Shock Q – If the resistance of your body were 100, 000 ohms, how much current would be produced in your body if you touched the terminals of 12V battery? Q – If the resistance of your body were 100, 000 ohms, how much current would be produced in your body if you touched the terminals of 12V battery? A – The current in your body would be 0.00012 A. (Why ?) A – The current in your body would be 0.00012 A. (Why ?)

28. Ohm’s Law and Electric Shock Q – If your skin were very moist so that you resistance was only 1000 ohms, and you touched the terminals of a 24V battery, how much current would you draw? Q – If your skin were very moist so that you resistance was only 1000 ohms, and you touched the terminals of a 24V battery, how much current would you draw?

29. Ohm’s Law and Electric Shock Q – If your skin were very moist so that you resistance was only 1000 ohms, and you touched the terminals of a 24V battery, how much current would you draw? Q – If your skin were very moist so that you resistance was only 1000 ohms, and you touched the terminals of a 24V battery, how much current would you draw? A – 0.024A (A very dangerous current) (Why?) A – 0.024A (A very dangerous current) (Why?)

30. Ohm’s Law and Electric Shock Q – If your skin were very moist so that you resistance was only 1000 ohms, and you touched the terminals of a 24V battery, how much current would you draw? Q – If your skin were very moist so that you resistance was only 1000 ohms, and you touched the terminals of a 24V battery, how much current would you draw? A – 0.024A (A very dangerous current) (Why?) A – 0.024A (A very dangerous current) (Why?)

31. DC or AC? DC – Direct current, electrons flow in one direction DC – Direct current, electrons flow in one direction AC – Electrons flow backwards and forwards. AC – Electrons flow backwards and forwards.

32. DC or AC Can convert AC to DC by the use of a diode in a electric current. Can convert AC to DC by the use of a diode in a electric current. A diode acts as a one way valve, allowing electrons to only pass through in one direction. A diode acts as a one way valve, allowing electrons to only pass through in one direction.

33. DC or AC The instantaneous speed of electrons is close to the speed of light. But this motion is in random directions. The instantaneous speed of electrons is close to the speed of light. But this motion is in random directions. The actual net speed of the current is quite slow as the electrons arte gently nudged through he wire due to the electric field set up inside the wire. The actual net speed of the current is quite slow as the electrons arte gently nudged through he wire due to the electric field set up inside the wire.

34. Electric Power The rate at which electrical energy is converted into another form such as mechanical energy. The rate at which electrical energy is converted into another form such as mechanical energy. Electric Power = current x voltage Electric Power = current x voltage

35. Electric Power Q – How much power is used by a calculator that operates on 8V and 0.1 amps? If it is used for 1 hour, how much energy does it use? Q – How much power is used by a calculator that operates on 8V and 0.1 amps? If it is used for 1 hour, how much energy does it use?

36. Electric Power Q – How much power is used by a calculator that operates on 8V and 0.1 amps? If it is used for 1 hour, how much energy does it use? Q – How much power is used by a calculator that operates on 8V and 0.1 amps? If it is used for 1 hour, how much energy does it use?