Current Electricity Chapter 51

Chemical energy converted to electrical energy in battery Energy is transferred There is a continuous and steady flow of charges in all parts of the complete circuit

An electric current An electric current is a flow of charge Conductors are substances which allow electric current to flow through ther freely. Insulators are substances which do not allow electric current to flow through them.

To show a Conductor or Insulator If the bulb lights upConductor If the bulb does not lightInsulator

Electric circuits A closed circuit is needed for current to flow. In order for a current to flow the circuit must be complete and there must be a potential difference or voltage between each end of the circuit.

A simple circuit containing bulb,battery and switch

Misconceptions Battery stores electricity Electricity from both ends of the battery Electricity is used up in a circuit Battery runs out of charged particles Battery runs out of electric current Battery supplies all of the charged particles Electric current gets used up in a bulb to make it work

Misconception Correct ideas Battery stores electricityBattery stores energy When a circuit is complete, this energy is released as chemical reactions occur in the battery, and causes a drift of charged particles in the circuit

Misconception Correct ideas Electricity from both ends of the battery Electric current is in one direction only in the circuit Electrons drift away from the negative terminal of the battery The other free electrons in the circuit drift in the same direction

Misconception Correct ideas Electricity is used up in a circuit Energy is transferred and converted to other forms of energy in the circuit For example, energy is transferred and converted in a bulb to heat and light

Misconception Correct ideas Battery runs out of charged particles Battery runs out of energy There are still charged particles in the battery, but the chemical reactions producing energy (and releasing electrons) in the battery can no longer occur

Misconception Correct ideas Battery runs out of electric current Battery runs out of energy This occurs when the chemical reactions that produce energy in the battery can no longer occur

Misconception Correct ideas Battery supplies all of the charged particles The charged particles originate throughout the circuit Charged particles throughout the circuit are set in motion by the battery when the circuit is complete The charged particles are part of the atoms that make up the wires, battery and bulb

Misconception Correct ideas Electric current gets used up in a bulb to make it work Energy is transferred in the bulb, and converted to heat and light The current leaving the bulb has the same value as the current entering the bulb, because the same number of electrons enters and leaves the bulb each second

Units used in Electricity Current is the flow of electrical charge. It is measured in Amps(A).Current (in amps) is given the symbol (I). Voltage, also called potential difference is the difference in electrical pressure needed for a current to flow.It is measured in volts (V). Resistance is the ability of a substance to resist the flow of electricity to flow through it. The unit of resistance is the ohm(  )

Relationship between current, voltage and resistance The larger the voltage, the larger the current that can flow. The larger the resistance, the smaller the current in the circuit. V = I x R I = V/R R = V/I

Ohm’s Law Ohm’s law states that the current flowing through a metallic conductor is proportional to the voltage across it, providing the temperature remains constant.

To verify Ohm’s Law In an electrical circuit, if the voltage is increased the current is also increased. i.e. Voltage = Constant Current The constant for each given conductor was later called the resistance of the conductor.The unit of resistance is the ohm(Ω)

Circuit used to demonstrate Ohm,s Law

Ohm’s law circuit using symbols

Plot of Voltage vs Current through the Origin

Series Circuit Bulbs connected in series are connected one after the other. The more resistance in the circuit the less current will flow. The more bulbs the dimmer each one will be. If one bulb is disconnected the circuit is broken

Series Circuit

Parallel Circuit Bulbs connected in parallel are connected side by side Each bulb is connected independently of each other. The total resistance in the circuit is much less than in a series circuit so the bulbs are brighter. If one bulb is disconnected the others continue to light.

Parallel Circuit

The 3 effects of electric current The three effects of electric current are: Heating effect Magnetic effect Chemical effect

Heating effect: The current has difficulty passing through the nichrome wire(high resistance) As a result heat is given off. Uses: Electric kettles, immersion heater, electric fires, toasters bulbs e.t.c

Magnetic effect When the switch is closed a current flows. The compass needle turns showing that there is a magnetic field caused by the current Uses: Electric motor, electromagnet

Chemical effect When an electric current is passed through water the water is chemically broken down into Hydrogen and Oxygen. This is called the electrolysis of water. The apparatus is the Hoffman Voltameter

Electrolysis of Water

TextbookChapter50-CurrentElectricity A1. Current,charge. A2. Conductors. A3. Negative,positive,positive,negative. A4. Potential,voltage,volts,voltmeter. A5. Current,amps,ammeter. A6. Resistance,ohms. A7. Resistors,resistance. A8. Larger. A9. Smaller. A10. Current,voltage,Ohm's. A11. Series. A12. Heating,magnetic,chemical.