Current. Electrons Flow - + Electrons are negatively charged and therefore flow from negative to positive e-

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Current

Electrons Flow - + Electrons are negatively charged and therefore flow from negative to positive e-

Current Current is the FLOW OF ELECTRONS AROUND A CIRCUIT In metals, current is carried by electrons We use an ammeter to measure current The unit of current is the ampere (A)

Current in a Series Circuit 2A The Current in a Series Circuit is the Same at Every Point

In a series circuit the bulbs are all the same brightness If the bulbs are of the same rating!

Current Questions ABC 1)The current reading for bulb B is 2A. What are the readings for bulbs A and C? 2) Bulb suddenly fails. What happens to bulbs A and C?

What Is the Current at This Point? 6A

If a cell is added the current will increase and the bulb gets brighter Brightness of Bulbs in a Series Circuit

If a bulb is added the current will decrease as there is greater resistance in the circuit and the bulbs get dimmer Brightness of Bulbs in a Series Circuit

Current in a Parallel Circuit A PARALLEL circuit has more than one path for the current to flow through Bulb A Bulb B Assuming both bulbs are the Same…they will be the same brightness

Current in a Parallel Circuit Bulb A Bulb B The Advantages of a parallel circuit are: If one bulb fails ….the other will remain on Both bulbs can be switched on separately

Current in a Parallel Circuit The total flow of current is equal to the total current from all of the branches 2A 6A

What is the ammeter reading? 3A 9A 3A

Voltage (Potential Difference)

Voltage Is the Driving Force That Pushes the Current Around the Circuit

Potential Difference/ Voltage This is VOLTA. He studied the driving force that pushes current around a circuit. He gave his name to the unit of Potential Difference The unit of Potential Difference is the VOLT (V)

Voltage in a Series Circuit 12V The voltage in a series circuit is shared across each component. The sum of the voltages across each component equals the source voltage 4V

What Is the Voltage? ?V?V 8V ?V?V

Voltage in a Parallel Circuit 6V The voltage is the same across all components in parallel

Complete the meter readings V1V1 V2V2 12V 6A A 2 A1A1 V3V3 A3A3

Which Is the Series and Parallel Circuit A * Current is THE SAME at any point * Voltage SPLITS UP over each component * Current SPLITS UP down each branch * Voltage is THE SAME across each branch B

Resistance

It can be calculated using Ohm’s Law: Resistance = Voltage (V) (Ohms)Current (A) V I x R Resistance is anything in a circuit that restricts the flow of current The unit of Resistance is the Ohm

Summary Table Current Is the flow of electrons around a circuit Voltage Is the driving force that pushes the current around. Resistance Is anything in a circuit which slows the flow down

Calculate the resistance 12V 3A ?

Electrical quantities in an electric circuit are related to each other by: OHM’S LAW OHM’S LAW says: If the source voltage remains constant, increasing the resistance in a circuit will cause a decrease in current flow in that circuit. In mathematical terms it tells us that current flow is inversely proportional to resistance. In equation form it says: Voltage (V) = Current (I) x Resistance (R) or V(in volts) = I (in amps) x R (in ohms)

Potential In volts (joules / coul) Current In amperes (coul / second) Resistance In ohms (volts / amp) Drop across a resistance Current passing through the resistor

V O L T A G E (volts ) Current (I) in amps II vv The slope of the Line gives the Resistance (Ω)

Factors Affecting Resistance 1.Thickness (diameter) of wire 2.Length of wire 3.Type of material 4.Temperature

Electron flow and Resistance Electricity in wires is a flow of electrons along the wire. As the electrons move along the wire they collide with the metal atoms. These collision make the atoms vibrate more…which makes the metal hotter. Resistance is a measure of how much a material tries to stop electricity passing through it.

CROSS SECTIONAL AREA -Thin wires have more resistance than thick wires -Halving (1/2) the cross sectional area of a wire doubles its resistance because there is half as much space for the electrons to move

Resistance - Length of Wire -Doubling the Length of a wire doubles its resistance because the electrons have twice as far to move

Type of Material Different materials have different resistances. Example: A nichrome wire has more resistance than a copper wire of the same size (the atoms in nichrome hold the electrons more tightly than copper atoms)

Temperature As temperature increases, resistance increases.

Voltage –current for a lamp V/voltsI / amps 00 0.50.04 1.00.08 1.50.12 2.00.15 2.50.18 3.0 3.5 0.19 0.20 Plot these results What do they show?

Current-Voltage Graphs Show Resistance I V A Filament Bulb As the temperature of the filament increases, the resistance increases – hence the curve

Current-Voltage Graphs Show Resistance I V A Diode Current will only flow through in ONE DIRECTION (It has very high resistance in the reverse direction)

There is a Balance…. If you increase the Voltage – then more current will flow If you increases the Resistance – then less current will flow

The Light Dependent Resistor 1A Dark 5A Light The resistance of the LDR depends on the amount of light falling on it. Its resistance decreases as the amount of light falling on it increases

The Thermistor 1A5ACOLD WARM The resistance of a thermistor depends on its temperature. Its resistance decreases as the temperature of the thermistor increases

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