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Physics > Electricity and circuits > Flashcards

Electricity and circuits Flashcards

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1
Q

What is current?

A

The rate of flow of charge of electrons.

-It will only flow through electrical components if there is a potential difference and the circuit is complete

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2
Q

What is potential difference?

A

The driving force that pushes charge. It is the energy transferred to a component per columb charge that passes through it

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3
Q

What is resistance?

A

How easy it is for current to flow through objects. It opposes current as current does work against resistance. This causes an electrical transfer of energy

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4
Q

What is the equation that links charge,current and time?

A

Charge (Q) - (C) = current (I) - (A) x time(T) - (S)

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5
Q

What is the equation that links current, potential difference and resistance?

A

Potential difference (V) = current (I) x resistance(R)

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6
Q

What affect does current have on a resistor?

A

As current flows through a resistor, it heats up due to collisions between electrons and ions in the lattice that makes it up. This is because the ions vibrate more making it harder for electrons to get through the resistor as there are more collisions (if too hot no current is able to flow)
-resistance increases with temperature

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7
Q

What is a ammeter?

A

Measures current (in amps) flowing through the component -can be put anywhere is a circuit

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8
Q

What is a voltmeter?

A

Measures potential difference across the component -it must be places in parallel with the component under test

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9
Q

What is Ohm’s law?

A

Current is directly proportional to the voltage when the temperature stays constant

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10
Q

What happens when investigation a filament lamp?

A

The current isn’t directly proportional to the voltage. This means it doesn’t follow Ohm’s law and the graphs isn’t straight.
-resistance is higher as greater voltages as temperature increases as the lamp heats up

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11
Q

What happens when investigating diodes?

A
  • current only flows in one direction and only when the voltage is about 0.6V
  • distance is much greater in one direction than the other
  • the graph is non-linear curved
  • doesn’t follow ohm’s law
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12
Q

What happens when investigating a thermistor and LDRs (resistors)?

A

Thermistors (temperature dependent resistor) have a low resistance at high temperatures
-used for temperature detectors e.g. car engines
LDRs (light dependent resistor) resistance decreases as light intensity increases
-used for automatic night lights
(BOTH FORM ASYMPTOTE GRAPHS)

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13
Q

What us a series circuit?

A

All components are connected in a line, end to end, between the +Ve and -Ve of the power supply (except voltmeters)

  • if you remove any component the circuit breaks and stops working
  • only one branch
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14
Q

What are the rules and patterns of series circuits?

A
  • more supply of V when there are more cells in the circuit
  • current is the same everywhere and is dependent of V and R
  • voltage of power supply is shared between components
  • resistance increases as resistors are added as they have to share V, this decreases current
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15
Q

What is a parallel circuit?

A

Each component is individually connected (except ammeters which are always in series). Therefore, if one is removed it will have hardly any affect on others.

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16
Q

What are the rules for parallel circuits?

A
  • potential difference is the same across all components
  • current is shared between branches
  • junctions are where the current splits and rejoins (total current into a junction is equal to total current leaving)
  • total resistance decreases if you add a second resistor as current has more than one way to flow (V=IR)
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17
Q

Where is energy supplied from in circuits?

A

Energy is supplied to the charge at the power source and the charge gives up this energy when it falls through any potential drop in components
-component offers a resistance so charges loose energy when they
go through it leading to a potential difference.
-larger the current or PD the more energy transferred to it

18
Q

What is the equation for energy transferred?

A

Energy transferred = current x voltage x time
Or
Energy transferred = voltage x charge

19
Q

What is power?

A

The rate of work done (how many joules of energy are transferred per second).
Total energy transferred depends on how long the appliance is on for and it’s power

20
Q

What is the equation for power and electrical power? And if you don’t have potential difference?

A

Power (W) = energy transferred(J) / time (s)
Electrical power (W) = current (A) x voltage (V)
- Electrical power (W) = current squared (A) x resistance (ohm’s)

21
Q

What is power rating?

A

Tells you the maximum amount of energy transferred between stores per second when in use
-the lower the power rating the less electricity used so it is cheaper to run

22
Q

What is A.C.?

A

Alternating current, where the movement of charges if constantly changing direction and are produced by alternating voltages (going between positive and negative)
-provided by mains power supply (230V) and frequency of 50Hz-electrical energy input

23
Q

What is D.C.?

A

Direct current where the movement of the charges is only in one direction created by direct voltage (either all positive or all negative)
-it is provided by batteries and cells -chemical energy input

24
Q

What is the neutral wire?

A

The blue wire which complete the circuit and where electricity usually flows out from

  • always goes to the left at 0V
  • goes to power station
25
Q

What is the live wire?

A

The brown wire which carries the voltage in and alternates between (+Ve and -Ve) of about 230V
- always goes to the right

26
Q

What is the earth wire?

A

Th yellow and green wire which is for safety and protecting the wiring
-it always goes to the top middle, is at 0V and carried the current away of their is a fault

27
Q

What are dangers of current?

A
  • electric shocks as body is at 0V making a large potential difference
  • fire due to huge current
28
Q

What is fusing?

A
  • a fuse is a built in weak point in a circuit that contains a thin wire with a higher resistance
  • when a large current flows it becomes too hot and melts, breaking the circuit and cutting off the live supply isolating the appliance
29
Q

How is the correct fuse chosen?

A

It is labelled with the maximum current that it will allow to flow through it.
-therefore, choose the fuse with the closest rating that us greater than the operating current

30
Q

What is earthing?

A
  • cables contain an earth wire to provide an alternate path for current if appliances develop faults
  • an earth wire is an essential for appliances with metal cases as an a.c. of just 0.1 A can kill you
  • therefore if the live wire becomes lose and touches it a large current flows to earth and blows the fuse breaking the circuit
31
Q

What are the features of a plug?

A
  • Cable is secured in the plug by a cable grip
  • the 3 pins are made from brass which is a good electrical conductor
  • there is a fuse between the live terminal and live pin
  • cases are made from tough plastic or rubber
32
Q

What is double insulting appliances?

A
  • means it has a plastic coating with no metal parts showing
  • this means it doesn’t need an earth wire
33
Q

What is conventional current?

A

A flow from positive to negative

34
Q

What is electron flow?

A

A flow from negative to positive

35
Q

What is the equation for total resistance in a parallel circuit?

A

1/R Total = 1/ R1 + 1/R2….

36
Q

What is the potential divider formula?

A

V out = V in x R1/R1 + R2

37
Q

What happens when an electrical current does work against a resistor?

A
  • thermal Energy is transferred to the resistor and the surroundings
  • this is because of collisions between electrons and ions in the lattice
  • low resistance wires and lower current reduces this
38
Q

What is the frequency and voltage of the UK domestic supply?

A

230V, 50Hz

39
Q

What can a circuit breaker and diode do?

A
  • diode can covert a.c. Into d.c

- circuit breaker can break the circuit to prevent current getting to high etc.

40
Q

What is a fixed resistors relationship with IV graphs?

A
  • current increases with increasing PD and resistance doesn’t change
  • directly proportional to PD hence following ohms law
  • direction of voltage doesn’t matter

Physics (14 decks)

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