electricity 2

Voltage, capacitance and current electricity.

what is the purpose of a residual current device

Rcd’s are trip switches that cut off current very quickly when a fault in an appliance causes a small current to flow to earth

what is the purpose of a miniture circuit breaker

MCb’s are used as safety devices, to prevent electrocution or fire by preventing too large a current flowing in the current

When will an Residual current device disconnect a circuit

when the difference in the value of the current between the live and neutral reaches a certain value(30mA) the RCD trips very quickly, disconnecting the circuit from the live

Which one of the following devices is adjusted when tuning a radio: transformer,diode,capacitor,rheostat

Capacitor( radios that are tuned using a dial rather than buttons have variabke capacitors in them. by adjusting the dial, you are varying the capacitance of the capacitor)

Define the volt

A potential difference of ! volt exists between two points when ! joule of energy is expended in moving 1 coulomb between them

WHat do MCB and RCD stand for

miniture circuit breaker

residual current device

Name the wire thst connects the fuse in a three-pin plug

the live/ brown wire

state and define the SI unit of capacitance

the SI unit of capacitance is the farad

a capacitance has a capacitance of 1 farad if placing a charge of coulomb on it raises the potential by 1 volt

Distinguish between Earthing and bonding in domestic electricity

Earthing means providing a path to Earth but Bonding means providing a path between objects

What is potential difference

The potential difference between two points is the work done in moving a charge of one coulomb from one point to the other or V=W/Q + notation

Describe an experioment that demonstrates the heating effect of an electric current.

Apparatus- Ammeter,heating coil, thermometer, power supply.

Procedure- 1.Set up apparatus as shown in diagram 2.Measure the initial temperature of the water.3. Switch on the power 4. Measure the current passing through the coil. 5. Allowing the current to flow for some time then turn off the power supply

observation and conclusion- There is a rise in temperature due to the current

Define Capacitance

C=Q/V where C is capacitance Q is Charge and V is the voltage across the capacitor

Describe an experiment to demonstrate that a capacitor can store energy

Apparatus- capaitor, battery(cell), bulb, switch, leads.

Procedure- 1.Connect battery to capacitor and close switch to charge the capacitor. 2. Open the switch, remove the battery, add a bulb to the circuit 3. close the switch

Observation- The bulv lights briefly, demonstarting that an energy conversion has taken place

Conclusion- The electrical energy stored in the capacitor was convertd to light energy

Describe what happens in the circuit when the 6V d.c. supply is replaced with a 6V a.c. supply

Current flows all continuously, as the capacitor constantly charges and discharges.

toasters have exposed metal parts. How is the risj=k of electrocution minimised?

The metal parts are earthed, the toaster could be double insulated, or an RCD or MCB could be used

what is electric current

electric current is the flow of electric charge

Hearing is one effect of an electric current. Give two other effects of an eletric current

Magnetic and chemical

A capacitor and battery are both sources of electrical energy. State two differences between a capacitor and a battery

Capacitors discharges faster than batteries. Capacitors store electrostatic potential energy whereas batteries store chemical energy. Battery give a constant current whereas the current dissipates very quickly with capacitors. Battery typically store mor energy

GIve one application of capacitors, other than in touchscreens

Source of energy in defibrillators. tuning circuits(radio). Camera flash.

how would an observer know that a wheatstone bridge is balanced?

there is no deflection in the galvonometer when it is balanced

the radiua of a wire is doubled. what is the effect of this on the resistance of the wire

The resistance decreases by a factor of four

Describe an experiment to demonstrate how the capacitance of a parallel-plate capacitor changes with the distance between the plates

Apparatus- Two metal plates, Van de Graff generator, gold leaf electroscope, leads.

Procedure- 1. set up apparatus. 2. Charge the plates by turning on the Van de graff generator. 3. Vary the distance between the plates

observation and conclusion- Increasing d leads to increasing divergence increasing voltage and decreasing Capacitance

what proporty of glass allows it to be used as a dielectric

glass is a good insulator

what would be the effect on the capacitance if the distance between two parallel plates in a parallel plate capacitor was doubled

it would be decreased by a factor of two

draw an electric field pattern in a charged parallel plate capacitor

List the factors that affect the capcitance of a parallel plate capacitor

A= common area of plates d = distance , e(wierd e ) permitivity (of dielectric)

list the factors that affect the heat produced in a current-carrying conductor?

R=resistance, I=current, t=time