4. Electricity and Magnetism Flashcards

Question

Static electricity - Eg. Balloon

Answer 1

- Rubbing the balloon causes the transfer of electrons from the jumper, leading to an imbalance of charges. - As one surface is negative and the other is positive, they attract. - Rubbing two balloons on the jumper causes the balloons to repel each other because they both have like (negative) charges. - Balloon is attracted to neutral wall bc relative to wall the ballon is more positive/ negative making the charges opposite. - Also the postive charged balloon will repel positive charges making the wall more negative + vice versa with negative balloon.

Answer 2

When two charged particles approach each other, they experience a force. The space in which an electric charge experiences a force is called an electric field. An electric field always points in the direction that a positive charge experiences a force.

Answer 3

Parallel electric field lines betewen two flat surfaces.

Answer 4

Measure of amount/rate of the flow of charges (eg. electrons). When charges are stationary, there is no current; when they move, there is a current.

Answer 5

Making each charged particle move faster Increasing the number of charged particles Increasing the amount of charge each particle carries.

Answer 6

I = Q/t I - Current (A, Amps) Q - Charge (C, Coulombs) t - Time (s, seconds) I = V/R V - Potential difference (V) R - Resistance (ohms)

Answer 7

Placing an ammeter IN the circuiot BETWEEN componenets/ the battery etc. Ammeters can be analogue (needle pointer) or digital (numbers).

Answer 8

- Conventional current is imagined flowing out of the positive terminal of a battery, around the circuit, to the negative terminal. - The charge carriers, however, are electrons, which have a negative charge. Electrons are repelled from the negative terminal of the battery and attracted to the positive terminal. - Electron flow is always in the opposite direction to conventional current.

Answer 9

- Alternating current (a.c.): electrons continuously change direction. - The voltage must reduce to zero and then become negative, causing the electrons to move in the opposite direction --> moving back and forth. - Direct current (d.c.): electrons flow in one direction only. - One level of voltage --> electrons flowing in one direction only

Answer 10

Measure of how much E.M.F. a battery has.

Answer 11

The work done or energy per unit charge around the whole circuit by an energy source, such as a battery. Measured in volts. - Phenomena that enables a charge to flow --> the electrical work done by a source in moving a charge around a complete circuit.

Answer 12

The energy needed per charge to flow between 2 points in a cirvuit. Work done per unit charge passing through a component.

Answer 13

(If circuit stays the same) EMF = Constant PD = Variable depending on points chosen within circuit

Answer 14

EMF (V, Volts) = Work done (J) / Charge (C) E = W/Q or V= W/Q

Answer 15

Voltmeter placed parallel aroudn a component - Can be analogue (needle-pointer) or digital PD - Voltmeter = parallel around points. EMF - Voltmeter = parallel around battery/ energy source.

Answer 16

A measure of the opposition to current flow within a circuit. Measured in ohms (Ω)

Answer 17

Resistance (Ω) = Potential difference (V)/ Current (A) R = V/I

Answer 18

Length / Cross-sectional area If length doubles --> resistance doubles (directly proportional) If cross-sectional area doubles --> resistance halves (Inversely proportional)

Answer 19

V = IR V = Voltage (V) I = Current (A) R = Resistance (Ω)

Answer 20

Power - Measure pf transfer rate of energy Original energy source in a circuit = chemical energy in battery. Electricity used to transfer chemical energy in battery to heat/ light/ kinetic energy.

Answer 21

P = IV P = Power (W or J/s) I = Current (A) V = Potential Difference (V)

Answer 22

E = IVt (bc P = E/t --> sub into P = IV formula) P = I²R (substituting V = IR into P = IV) P = V²/R (substituting I = V/R into P = IV)

Answer 23

1 kW = 1000 W E (J) = P (W) * T (s) E (kWh) = P (kW) * T (h) (used when units are too high)

Answer 24

- Use straight lines to represent wires - Place voltmeters in parallel with the components - Place ammeters in series with components - Use conventional electrical symbols to represent the components, not real-life images.

Answer 25

Function - Opens/ closes circuit Application - Turns devices on/ off

Answer 26

Function - Provides direct current (d.c.) Application - Store of energy

Answer 27

Function - Series of cells Application - Larger store of energy than one cell

Answer 28

Function - Transfers energy into light Application - Lighting

Answer 29

Function - Breaks circuit if too much current Application - Safety device

Answer 30

Function - Measures potential difference

Answer 31

Function - Measures the current

Answer 32

Function - Resists flow of electrons Application - Limits the current

Answer 33

Function - Changes resistance and thereby changes current Application - Dimmer switches

Answer 34

Function - Resistance decreases as temperature increases Application - Temperature switches or thermostats

Answer 35

Function - Transfers electrical energy into heat energy Application - Heating a room/space

Answer 36

Function - As light intensity increases, resistance decreases Application - Light sensors

Answer 37

Function - Switch operated by a magnet Application - Control high-power circuits with low-power inputs

Answer 38

Function - Increases or decreases voltage Application - Efficient electricity supply

Answer 39

Function - Varies resistance at a point with a sliding contact Application - Sensory circuits

Answer 40

Function - Produces a magnetic field when current flows Application - Relays, electromagnets, solenoids

Answer 41

Function - Provides an alternating current Application - A store of energy

Answer 42

Function - Uses current to make some spinning motion Application - Store of kinetic energy

Answer 43

Function - Uses kinetic energy to produce a current Application - Generating electricity

Answer 44

Function - Allows current to flow in only one direction Application - Safety devices

Answer 45

Function - Emits light of a specific colour when current flows. Application - Low energy lighting

Answer 46

One loop of wire --> no brances

Answer 47

Voltage of each component adds up to voltage of battery Vtotal = V1 + V2 + V3 eg. Battery = 6V Light bulb 1 = 2V Ligh bulb 2 = 4V (difference between 1 and 2 is due to resistance of components)

Answer 48

Current is constant across circuit. Itotal = I1 = I2 = I3 etc.

Answer 49

Resistance of componenets adds up to toal resistance Rtotal = R1 + R2 etc.

Answer 50

EMF added up to form total voltage for battery (multiple cells)

Answer 51

Circuit with loops. Branches divide into two wires forming two loops.

Answer 52

Each branch of the parallel circuit recieves voltge equal to the power supply. Vtotal = V1 = V2 = V3 (if V1, V2 and V3 are located on different loops with only one component on each loop)

Answer 53

Current splits at each branch in the circuit based on the resistance of the branch. Itotal = I1 + I2 (total current flowing into junction = total current flowing out of junction --> bc current 'joins up' again)

Answer 54

1/Rtotal = 1/R1 + 1/R2 + 1/R3

Answer 55

An e.m.f. will be induced in a conductor in the presence of a changing magnetic field.

Answer 56

- When a coil of wire is placed around a magnetic material, the current flowing through the magnetic material, aligns the domains temporarily, making it magnetic. - A wire close to a changing magnetic field will experience an induced EMF force. (magnetic field creates a force on the electrons creating induced EMF + current)

Answer 57

- Moving a magnet so its field lines are cut by wire. - Moving a wire across a magnetic field.

Answer 58

- Current, Motion of wire, Direction of mag. field. Thumb + pointer + middle finger perpendicular to each other. thuMb represents Motion of wire (relative to field <-- ask Mr. Gardiner what that means) First finger represents direction of magnetic Field seCond finger represents direction of Current (conventional) Bc current used in conventional, to work out direction of electron flow --> reverse current.

Answer 59

Coming out of page

Answer 60

Going into page

Answer 61

- A magnetic field is created when an electric current (charge) flows through a wire. - DC --> constant magnetic field - AC --> alternating magnetic field - Magnetic field around a current carrying wire is circular + perpendicular to wire (get's weaker the further away from wire)

Answer 62

Thumb pointing upwards - Direction of current Fingers curled inwards (curling around wire) - Direction of magnetic field Current used is conventional. To figure out direction of electron flow, reverse current.

Answer 63

- Two stationary magnetic poles - Soft iron core with copper wire coil (armature/coil) found in between magnetic poles) - Slip ring attatched to coil that rotates with it. - Carbon brushes in contact with slip ring at all times

Answer 64

- Kinetic energy causes the armature to spin. - An EMF is induced when a wire moves through a magnetic field. - Therefore as the armature spins, an EMF is induced due to the movement through the magnetic field. - The EMF pushes the electrons, causing them to move. This creates a current flow through the armature. - The current flows through the armature into the slip rings and then through the carbon brushes when in contact. - The changing direction of the armature results in a positive and negative EMF, which results in an alternating current.

Answer 65

During a full rotation of the armature, a large range of EMF's are produced. At 0 turns (Sides of armature are moving parallel to mag. field), the EMF is 0 At 1/4 of a turn (Sides of the armature are moving perpendicular to the mag. field) = Max EMF produced At 1/2 of a turn (Sides of armature are moving parallel to mag. field) = EMF is 0 At 3/4 of a turn (Long sides of armature are moving perpendicular to mag. field but in opposite direction. --> Max EMF produced but in opposite direction (caused change in current direction) At 1 turn (Sides of armature are parallel to mag. field) --> EMF is 0.

Answer 66

provide a constant magnetic field across the coil

Answer 67

- Usually made from many turns of wire (Iron core with a copper wire wrapped around it) - It is rectangular so that its sides are perpendicular to the magnetic field.

Answer 68

- Cylindrical conductors that make constant contact with the coil during rotation - They allow the direction of the induced electromotive force (e.m.f.) to alternate and therefore cause an alternating current (a.c.)

Answer 69

Make an electrical connection between the rotating coil and a circuit, avoiding the wires becoming twisted

Answer 70

- Damaged insulation - Overheating of cables and appliances - Overloading sockets - Damp conditions

Answer 71

- Electrical wires + cables are covered with an insulator (eg. PVC plastic). - If the insulator is damaged and you touch live wire you cna be electrocuted

Answer 72

Large current running through appliances = heat. Too much heat can cause a fire.

Answer 73

- Too many appliances / too many extension adapters draws too much current through one socket. - Can overload the socket which can result in a fire.

Answer 74

- Water conducts elecrticity - By touching an lecetrical appliance when wet or with damp gans you can be electrocuted. (Electrial devices in damp conditions need to be specifically designed for such)

Answer 75

- Always use appliances such as pliers/wire cutter with PLASTIC HANDLES (used for relatvely small voltags) - Never move any object close to a large potential difference.

Answer 76

- Circuit distributing electricity around your house. - Outside of the cable is made of an insulating plastic + contains three smaller wires with insulating plastic around them too. - Live wire - Earth wire - Neutral wire (The wires have different colours due to Europe guidelines + regualtions)

Answer 77

Brown - Carries current from the main supply. - On/Off switch connected to this wire bc it's the source of current.

Answer 78

Blue - Completes the full circuit - Doesn't supply current

Answer 79

Green + Yellow striped - Safety feature used to prevent electrocution

Answer 80

- Earth wire is connected to the outer metal casing of an appliance + prevent lethal shock if a fault makes teh casing live. - Earth wire provides a path for current to flow to earth (ground) - This happens bc the wire has a lower resistance than the person.

Answer 81

- Protects a circuit - Has a thin wire inside it connected to the live wire. - If too much current flows through teh live wire, the wire melts (the 'fuse blows') and breaks the circuit (turning off the electrical device) - Fuses are designed to blow at different current ratings. (The rating of the fuse must be the lowest value that is still greater than the amount of current the appliance is designed to use)

Answer 82

- Safety device similar to dues - If the amount of current flowing between the live and neutral wires increases rapidly --> trip switch detects this + opens a switch to break the circuit. - Rating/ value of trip switch has to be slightly above the amount of current the appliance is designed to use. - Trip switch breaks circuit quickly (unlike fuse) - Can also be reused by switching it back on.

Answer 83

Wire arranged as a coil --> causes magnetic field bc of the magnetic fields created by current flowing through a wire. The magnetic fields 'combine' and create a magnetic field identical to a bar magnet (The field is strongest inside the solenoid (coil) bc the field lines are densest there)

Answer 84

- Increase the current through the solenoid. - Increase the no. of turns of wire in the solenoid - Placing a soft iron core in the middle (concept of electromagnets)

Answer 85

Supplying a coil with AC --> results in changing the direction of the current --> thus diretion of the magnetic field every half cycle.

Answer 86

- Increase current in the wire. - Increase no. of individual wires. - Increase strength of magnetic fields. - Increase length of the wire within the magnetic field. (Changing the direction of the magnetic field or current changes the direction of the force)

Answer 87

- Direction of Force, Current, Field First finger = Field (N to S) seCond finger = Current (conventional) thuMb = Movement (Force) If calculating force on negatively charged particle, reverse current direction.

Answer 88

North + south poles of a magnet with gap between. Armature/ coil of wire in the middle. Coil connected to split ring. Split ring connected to carbon brushes. Carbon brushes connected to power supply.

Answer 89

When a wire moves through a magnetic field a force is induced --> causing the wire to move. There are two magnetic poles with a coil between them. - The direction of the mag. field stays constant. - If the side of the coil closest to the north pole, is constantly supplied with current in one direciton, it will constantly experience a force in one direction. Due to the split ring this can happen and this causes the armature to spin, thus converting electrical energy into kinetic energy.

Answer 90

As the coil rotates, the direction of current needs to stay the same so that the force also acts in the same direction. (Fleming's left hand rule) - The commutator spins with the wires. - Brushes make contact with part of the split ring, when it spins the brushes make contact with other part of split ring. Once the coil has rotated through 180°, current continues to flow in the original clockwise direction causing the force on the left side to be up, and the force on the right side to be down - This means the north side of the DC motor always gets teh current in one direction, meaning that side will always have a downwards force.

Answer 91

- Increase the current - Increase teh strength of the magnetic field - Increase the no. of turns in the coil.

Answer 92

A device that can increase size of an alternating electromotive force (e.m.f) Two types of transformers - Step-up transformer - Step-down transformer

Answer 93

Increases voltage More turns on the secondary coil than on the primary coil

Answer 94

Decreases voltage More turns on the primary coil than on the secondary coil.

Answer 95

- Primary coil through which A.C. is supplied (energy source of transformer) - Soft iron core --> allows induction of alternating magnetical field which can induce an AC current in secondary coil. - Secondary coil is the output of the transformer. No of coils decides the type of transformer.

Answer 96

Vp/Vs = Np/Ns Vp - Voltage in primary coil Vs - Voltage in secondary coil Np - No. of turns in the primary coil Ns - No. of turns in the secondary coil.

Answer 97

Vp*Ip = Vs*Is Vp = Voltage in primary coil Ip = Current in primary coil Vs = Voltage in secondary coil Is = Current in secondary coil

Answer 98

- The primary coil is supplied with an alternating current and behaves like a bar magnet that is constantly switching its poles due to the constantly changing current (a bit like a rotating bar magnet). - A constantly changing magnetic field is transferred to the secondary coil via the soft iron core. - Because we now have a conductor (secondary coil) in the presence of a changing magnetic field, an electromotive force (e.m.f.) is induced across the secondary coil. - The e.m.f. induced across the secondary coil is also constantly changing and therefore provides an alternating current.

Answer 99

Efficiency of transformers = Pout/Pin = (Is*Vs/Ip*Vp) * 100%

Answer 100

- Using low resistance coils to reduce the power wasted due to the heating effect of the current. - Using a laminated core (Layers of iron separated by layers of insulation) --> reduces heating in the iron core + prevents currents from being induced in the core itself (referred to as eddy currents).

Answer 101

- Power has to be conserved - P = IV Therefore if voltage increases, current decreases to compensate. Therefore at a high voltage, current is low. Decreasing current, decreases heat loss.

4. Electricity and Magnetism Flashcards

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