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Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q
  1. For a charge to flow…
  2. current def
  3. charge equation
A

there must be a closed circuit and source of potential difference (battery/cell)

current is the flow of charge

Q = It

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2
Q

voltage equation

A

V = IR

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3
Q

what kind of graph if resistance is constant?

A

linear because current is directly proportional to voltage

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4
Q

when is IV graph non-linear?

A

lamps, diodes, thermistors and LDRs bc the resistance is not constant (changes with current through the component)

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5
Q

How does resistance change with current?

A
  1. As resistance decreases, current increases
  2. because when current increases, the electrons have more energy
  3. so when they flow through the resistor, they collide with the atoms in the resistor which transfers energy to the atoms,
  4. making them vibrate more, making it harder for electrons to flow through
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6
Q

How does resistance change with temperature in:
1. normal wires
2. thermistors
AND what are thermistors used in?

A
  1. in normal wires its the same as with current so as current increases, resistance decreases
  2. in thermistors, the hotter the temp the lower the resistance
  3. thermistors are often used in temp detectors/thermostats
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7
Q

How does resistance change with length?

A

the longer the wire, the higher the resistance because the electrons have to make it through more resistor atoms

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8
Q
  1. How does resistance change with light (LDR)?
  2. AND what are LDRs used in?
A
  1. The higher the light intensity, the lower the resistance
  2. LDRs are used in automatic night lights
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9
Q

How does resistance change with voltage (diodes)?

A

a diode allows current to flow freely in one direction so in the opposite direction, there is lots of resistance

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10
Q

Series circuit:
1. current
2. Potential difference
3. resistance
3. total resistance equation

A
  1. current is the same everywhere
  2. pot dif is shared across the circuit (PD of power supply = sum of PD across components)
  3. resistance is the sum of the resistance in each component because the charge has to push through both of them
  4. R(t) = R(1) + R(2)
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11
Q

Parallel circuit:
1. current
2. Potential difference
3. resistance
4. resistance equation

A
  1. current splits at junction and then joins back up
  2. potential difference is the same everywhere because charge can only pass through one branch
  3. total resistance is less than the branch with the smallest resistance because the charge has multiple branches to take so only some charge will flow through each branch
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12
Q

Mains electricity:
1. AC or DC
2. frequency
3. voltage

A
  1. AC
  2. 50Hz
  3. 230V
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13
Q

Live wire:
1. colour
2. Voltage
3. what does it do
4. dangerous?

A
  1. brown
  2. 230V
  3. carries the alternating pot dif from the supply
  4. could be dangerous even if mains circuit is off because current may still be flowing through it
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14
Q

Neutral wire:
1. colour
2. voltage
3. what does it do?

A
  1. blue
  2. 0V
  3. completes the circuit
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15
Q

Earth wire:
1. colour
2. voltage
3. what does it do

A
  1. green and yellow stripes
  2. 0V
  3. safety wire to stop the appliance becoming live if there is a fault, the very high dangerous current flows through it and into the ground, melting the fuse which breaks the circuit
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16
Q

Power:
1. definition
2. unit
3. directle proportional to…
Two equations:
4. Energy =
5. Energy =

A
  1. power if the energy transferred per second
  2. Watts, W
  3. directly proportional to current and voltage
  4. E = Pt
  5. E = QV
17
Q

national grid:
1. step up transformers
2. step down transformers

A
  1. step up - increase PD and decrease current so less energy is lost
  2. step down - decrease PD and increase current for domestic appliances
18
Q

If a body has the same amount of positive and negative charge…

A

they cancel out, forming a neutral body

19
Q

Static electricity - explain

A
  1. when 2 insulators are rubbed together, electrons are transferred from one object to the other
  2. this forms a positive charge on one object and a negative on the other
20
Q

why does static electricity only happen with insulators?

A

conductors always have electrons flowing through them, cancelling any effect
insulators become charged because the electrons cannot flow

21
Q

When does sparking occur?
What is sparking?

A
  1. when enough charge builds up and the objects are close but not touching
  2. the spark is when the charge jumps from the highly negative object to highly positive object to balance out the charges
22
Q

Electrostatic force (3 things)

A

greater charge = greater force
closer together = greater force
noncontact force

23
Q

Unit for:
1. current
2. charge
3. resistance
4. potential difference
5. power

A
  1. current = amps, A
  2. charge = coulomb C
  3. resistance = ohm
  4. potential difference = volts, V
  5. power = Watts, W
24
Q

Definitions:
1. (electrical) Current
2. ohmic conductor

A
  1. the rate of flow of (electrical) charge
  2. a conductor whose current flow is directly proportional to pot dif across it, when held at constant temp

Physics (10 decks)

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