Electricity

Question 1

There are positive and negative electrical charges. Positive repels positive and negative repels negative but positive and negative attract

Question 2

Electrical charge is measured in coulombs

Question 3

An electrical field is a region in which an electrical charge experiences a force

Question 4

Electrostatic charges can be produced by friction e.g. rubbing a balloon on your hair
The charging of so,ids by friction involves a transfer of negative charge (electrons)

Question 5

The direction of an electrical field at a point is the direction of the force on a positive charge at that point

Question 6

An electrical field around a point charge shows arrows pointing away from the centre point

Question 7

An electrical field between two oppositely charged plates shows a flow from the positive to the negative charge

Question 8

To distinguish between electrical conductors and insulators, form a simple circuit with an ammeter and add certain objects. If the ammeter gives a reading then it is a conductor, otherwise an insulator

Question 9

Conductors contain free electrons that pass on electrical currents, such as metals, or ionic solutions. Insulators do not such as wood or rubber.

Question 10

Electrical current is the rate of flow of charge, or the charge passing a point per unit time. I =Q/t

Question 11

Ammeters are always connected to a circuit in series, and analogue ammeters must be used to the correct range (see 4th form electricity notes)

Question 12

Conventional current flows from positive to negative and the flow of free electrons is negative to positive

Question 13

Electromotive force (e.m.f.) is the electrical work done by a source in moving a unit of charge around a circuit. Measured in volts.
E=W/Q (work done/charge)

Question 14

Potential difference in the work done by a unit charge passing a component, measured in volts.
V=W/Q

Question 15

Voltmeters should always be connected in parallel to the component.

Question 16

Resistance: R =V/I

Question 17

To determine an objects resistance, use a fixed current using an ammeter, and measure the voltage across a component. Then use the formula to find the objects resistance

Question 18

Current voltage graphs of a resistor, a filament lamp, and a diode.

Question 19

For a metallic wire, resistance is directly proportional to the length of the wire, and inversely proportional to cross-sectional area

Question 20

All electrical circuits transfer energy from a cell or mains supply, to the circuit components, and then the surroundings.

Question 21

Electrical power , P = IV

Question 22

Electrical energy (because energy = power x time)
E=IVt

Question 23

The kilowatt hour is the energy equivalent to the consumption of 1000 watts in one hour
Practice cost of using appliances calculations

Question 24

Be able to draw circuits involving all symbols(see third form notes)

Question 25

Current is the same at any point in a parallel universe circuit, while in a parallel circuit current is divided among branches. In a parallel ciruit the sum of currents entering a junction is the same as the sum of currents leaving a junction.

Question 26

Each resistor in parallel receives the same voltage as the battery, while in series the batteries voltage is divided among components depending in resistance

Question 27

For resistance, the combined resistance of two resistors in parallel is less than either resistor by itself. In series R total = R1 + R2 In parallel 1/R total = 1/R1 + 1/R2

Question 28

Connecting lamps in a parallel ciruit is advantageous as there is less resistance in total so the circuit requires less energy. Also if one branch breaks then the other branches will continue to work, unlike in series