T2 current, potential difference and resistance Flashcards

1
Q

what is electric current

A

flow of electrical charge

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2
Q

equation linking charge, current and time

A

Q = I t

charge (C), current (A), time (s)

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3
Q

what can be said about the value of current at any point in a single closed loop

A

current is the same at all points in a closed loop

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4
Q

what 2 factors does the current in a circuit depend on

A
  1. Potential difference (V)

2. resistance (R)

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5
Q

equation for potential difference if current and resistance are known

A
V = I R
potential difference (v), current (A), resistance (ohms)
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6
Q

what is an ohmic conductor

state the condition required

A
  • conductor for which current and potential difference are directly proportional
  • resistance remains constant as current changes
  • temperature must be constant
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7
Q

list 4 components for which resistance is not constant as current changes

A
  1. lamps
  2. diodes
  3. thermistors
  4. light dependant resistors (LDRs)
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8
Q

what happens to resistance of a filament lamp as the temperature increases

why

A
  • resistance increases
  • ions in metal have more energy, so vibrate more, causing more collisions with electrons as they flow through the metal, creating greater resistance to current flow
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9
Q

what is different about current flow through a diode

A
  • current only flows in one direction

- resistance is very high in the other direction, preventing current flow

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10
Q

state what happens to the resistance of a thermistor as temperature increases

A

thermistor’s resistance decreases

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11
Q

give 2 examples of when a thermistor may be used

A
  1. thermostat to turn a heater on below a certain temperature
  2. freezer to turn on a cooler when the temperature becomes too high
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12
Q

state what happens to the resistance of a LDR as light intensity decreases

A

LDR’s resistance increases

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13
Q

give an application for a LDR

A
  • street lights often use LDRs

- when light levels become too low, the light gains sufficient current to turn on

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