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Physics > P4/5: Electricity > Flashcards

P4/5: Electricity Flashcards

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1
Q

What is static electricity?

A

when charge “builds up” on an object and then stays ‘static”

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2
Q

How does static electricity cause objects to attract? (3)

A
  • electrons are moved from one material to another
  • making one material + charged and the other - charged
  • so they attract
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3
Q

what causes the attraction between protons and electrons ?

A

the electric force caused by the charge

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4
Q

what is current? Equation?

A

measurement of HOW FAST charge transfers energy.

current = charge/time
I = Q/t
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5
Q

what is voltage? Equation ?

A

measurement of how much ENERGY the charge transfers

voltage = energy/charge
V = e/Q
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6
Q

What direction does current flow from?

A

negative -> positive

negative charge flowing in the anticlockwise direction is a + current!

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7
Q

What will happen to the total current supplied, as more resistors are added IN SERIES/ IN PARALLEL?

A

decreases

increases - more paths for current so current increases

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8
Q

how does a voltmeter measure voltage?

A
  • the 2 ends of the voltmeter are connected across the device (in parallel)
  • measures the difference in current’s energy between the two wires
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9
Q

what is ohm’s law?

A

current in a METALLIC conductor at FIXED TEMP is directly proportional to applied VOLTAGE

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10
Q

What is Emf ?

A

a voltage input : batteries, generators

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11
Q

What is resistance ? Equation?

A

resistance is anything that opposes electrical current.
measures how many volts are needed to cause 1 amp of current.
V = IR

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12
Q

What will happen to the TOTAL circuit resistance as more resistors are added in SERIES/PARALLEL?

A

INCREASE

DECREASE - more path for current so current increases, resistance decreases

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13
Q

In series, which of current/voltage stays the same and which adds up to equal the total supplied ?

A

CURRENT - STAY THE SAME

VOLTAGE - ADDS UP TO EQUAL TOTAL VOLTAGE SUPPLIED

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14
Q

In PARALLEL, which of current/voltage stays the same and which adds up to equal the total supplied ?

A

CURRENT : ADDS UP TO EQUAL TOTAL CURRENT SUPPLIED

VOLTAGE : STAYS THE SAME

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15
Q

what is electrical power? equation?

A

the power of an electrical device is the rate at which electrical energy is transferred in a circuit.
rate of the transfer of electrical energy.

meaning : p = e/t

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16
Q

Equation for power in a circuit?

A 
power = voltage x current
P = IV
17
Q

What happens to the current and resistance when voltage increases in a filament lamp?

A

Voltage increases, so bulb get HOTTER
So the resistance INCREASES
current DECREASES

18
Q

How do diodes affect current?

A

They only let current go in ONE DIRECTION.

The resistance is VERY HIGH in the other direction.

19
Q

How does temperature affect resistance? (2)

A

As temp increases, the metal atoms SHAKE MORE.
This makes it difficult for DELOCALISED ELECTRONS to flow.
So RESISTANCE INCREASES as TEMP INCREASES.

20
Q

What do LDRs and Thermistors do and how does it affect resistance?

A

LDR - LIGHT energy is ABSORBED CREATING MORE FREE ELECTRONS
Thermistor - HEAT energy is absorbed creating more free electrons

The free electrons mean MORE CURRENT SO RESISTANCE DECREASES, with MORE LIGHT/HEAT

21
Q

A length of wire increases, resistance….

A

INCREASES

22
Q

What is DC current ?

A

Direct current - only flows in 1 direction

batteries supply DC

23
Q

What is AC current?

A

Alternating current - Curren changes direction 50X PER SECOND (frequ: 50Hz)
Mains electricity supply AC

24
Q

What is the national grid?

A

A system of power cables, transformers connecting us to power station so electricity reaches CONSUMERS

25
Q

How can energy loss be reduced when electricity is transmitted over long distances?

A

by increasing voltage, the same amount of power can be transferred using less current which heats up wires

26
Q

How can we calculate energy loss in a wire of resistance?

A

Power = I^2 R

27
Q

what are step up and step down transformers ?

A

Machines that increase/decrease voltage of AC current .

28
Q

what does a kilowatt-hour (kWh) measure?

A

Energy

29
Q

What colour are the wires in a plug and what do the wires do?

A

Brown - live - carry alternating voltage from the supply to the circuit
Blue neutral - forms opposite end of circuit to live wire to complete circuit
Green/yellow - earth - safety

30
Q

What happens if the live wire touches the metal case and how does the earth wire and fuse prevent the mains cable from heating up/causing fire.

A

The case willl be electrified so any who touches it will get electrocuted

a current goes from live wire to earth wire.
curing fuse to melt.

31
Q

explain why voltage is stepped up by transformers?

A
  • A higher voltage means less current
  • therefore less energy lost in transmission
  • because power is lost , p=I^2R
  • SO TRANSFER IS MORE EFFICIENT
32
Q

what happens when 2 or more resistors are in parallel and why?

A

The combined resistance decreases and is lower then the lowest resistance of one

this is because voltage is same for every component, but there are more paths for current to pass through, meaning more current. This decreases resistance.

33
Q

What is meant by zero error?

A

Any indication that a measuring system gives a false reading when the true value of a measured quantity is zero

34
Q

Am electrician replaced a switch.

The electrician could have gotten electric shock unless circuit is disconnected from supply . Explain why (3)

A
  • one wire in switch is live
  • electrician is earthed
  • so large pd between live wire and electrician
35
Q

describe a method to investigate I-V characteristics of a fixed resistor?

A
  1. Use one fixed resistor
  2. Vary the potential difference across the component using the variable resistor
  3. For each value of potential difference, record the reading of current
  4. Take repeat readings and calculate a mean
  5. Turn off the power supply between measurements to prevent the wires from heating
  6. Reverse the terminals of the power supply to repeat at negative values of potential difference
36
Q

when do sparks occur?

A

when 2 object are oppositely charged / have surplus electrons
- so electrons jump to an object that is neutral

37
Q

why is charge not static in conductors (metals)

A

any charge would pass through the metal to the earth

Physics (11 decks)

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