unit 2 electricity

Question 1

what is current

Answer 1

• measured in amperes/amps (A)
• is the rate of flow of charge at a point in the circuit
• in metals, current is the flow of electrons, but in solutions, can be flow of ions
• conventional current is the flow of positive charge (opposite direction to flow of electrons as electrons are negatively charged)
• current is conserved at a junction in a circuit because charge is always conserved
• current is measured with an ammeter connected in series with the component

Question 2

What is resistance?

Answer 2

• measured in Ohms

- the greater the resistance, the harder it is for current to flow through the component

Question 3

What is voltage?

Answer 3

• potential difference, measured in volts (V) (Voltage where 1 Volt = 1 joule/coloumb)
• potential difference (a.k.a Voltage) is defined as: the amount of energy transferred per unit of charge passing through the terminals
• it is measured by a voltmeter placed in parallel across the components
• the higher the voltage, the higher the current

Question 4

what happens to current when resistance is changed in a circuit

Answer 4

• lower resistance means higher current

- higher resistance means lower current

Question 5

what is a light-dependant resistor (LDR)

Answer 5

• an LDR has a resistance that changes when light is shone on it and its resistance decreases
• resistance of an LDR DECREASES as the light intensity increases

Question 6

what is a thermistor

Answer 6

• a resistor who’s resistance changes quite a lot even with small changes in temperature
• resistance of a thermistor DECREASES as temperature increases

Question 7

how can lamps and LEDs be used to indicate the presence of a current in a circuit

Answer 7

when a small current flows though them, the light will be much dimmer than if a large current flows through them

Question 8

examples of the dangers of electrostatic charges

Answer 8

• as aircraft fly through the air, friction causes them to become charged statically. after the aircraft lands, there is a chance of the charges escaping to the earth as a spark or flash of electricity- could cause explosion. solution: earth plane with a conductor as soon as it lands and before refuelling
• fuel tankers on roads must be earthed before fuel is transferred, to prevent sparks causing a fire of explosion

Question 9

examples of uses of electrostatic charges

Answer 9

• ink jet printers- use electrostatic charges to direct a jet of ink drops onto paper. each drop of ink is given charge so that as it falls between a pair of deflecting plates, electrostatic forces guide it to the correct position
• photocopiers- page 90