Current and Voltage

Starter How do we measure electrical charge (Q)?

Units of Electric Current Electric current is measured in Amps (A) Very small currents can be measured in milliamps (mA) 1000mA = 1A 500mA = 0.5A 1mA = 0.001A

Current Electric current is measured in units called amps (A). The electric current is not used up by the components in a circuit but it transfers energy from the voltage source to the various components making up the circuit. Electric current is measured using an ammeter.

Current Electric current is measured in units called amps (A). The electric current is not used up by the components in a circuit but it transfers energy from the voltage source to the various components making up the circuit. Electric current is measured using an ammeter. The ammeter is placed in series within the circuit.

Current in a series circuit If the current here is 2 amps… The current here will be… The current here will be… And the current here will be… In other words, the current in a series circuit is THE SAME at any point

Measuring current I Set up the circuit shown below…… …and then record the current using an ammeter in the places shown below. What do you notice about the readings? The current is the same for each ammeter. A

Current in a parallel circuit A PARALLEL circuit is one where the current has a “choice of routes” Here comes the current… Half of the current will go down here (assuming the bulbs are the same)… And the rest will go down here…

Measuring current II A1 A2 A3 0.8 A4 0.4 0.4 0.8 For a parallel circuit, the current that leaves the cell or battery is the same as the current that returns to the cell or battery. The current does not get used up by a circuit, just the energy the electrons are carrying. At the junction of the circuit we say that current is conserved. A1 = A4 …then record the current at the locations shown. What do you notice about the readings? Set up the circuit shown below…… Ammeter Current (A) A1 A2 A3 A4 A1 A4 0.8 A2 0.4 A3 0.4 0.8 The sum of the currents in the branches of a parallel circuit is the equal to the current that leaves the cell or battery. A1 = A2 + A3 =A4

Current in a parallel circuit (with identical bulbs) If the current here is 6 amps And the current here will be… The current here will be… The current here will be… The current here will be…

Use the following interactive animation to check your understanding of current and voltage in different circuits.

Measuring Potential difference (voltage) Potential difference is measured using a voltmeter. The voltmeter is placed in parallel to the circuit.

Measuring voltage I V1 V2 V3 1.5 0.75 0.75 For a series circuit, the sum of the voltages for each component is equal to the voltage across the cell or battery. V1 = V2 + V3 Set up the apparatus as shown…… …then record the voltages at the locations shown. What do you notice about the readings? V1 Voltmeter Voltage (V) V1 V2 V3 1.5 NB Voltmeters are connected in parallel 0.75 0.75 V2 V3

Series circuit

Measuring voltage II V1 V2 V3 1.5 1.5 1.5 What do you notice about your readings? For a parallel circuit, the voltage across the cell/battery is the same as the voltage across each branch. V1 = V2 = V3 ..measure the voltage at the locations shown. Set up the apparatus as shown…. V1 V2 Voltmeter Voltage (V) V1 V2 V3 1.5 V3 1.5 1.5

Parallel circuits

What is potential difference (voltage)? It is the energy transferred per unit charge passed and hence that the volt is a joule per coulomb.

Plenary – P2.4c