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physics paper 1 > Electrical Current > Flashcards

Electrical Current Flashcards

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1
Q

Describe Current, Voltage and Resistance in a Series Circuit

A
  • Current - same everywhere in the circuit
  • Voltage - shared across all components in the circuit
  • Resistance - shared across all components in the circuit
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2
Q

Describe Current, Voltage and Resistance in a Parallel Circuit

A

Current - shared across each branch in the circuit

Voltage - same across each branch in the circuit

Resistance - = 1 / RT = 1 / R + 1 / R + 1 / R …

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3
Q

What is Power

A

The energy transferred per second

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4
Q

What are the Power Equations

A
  • P = IV

Power (W) = Current(A) x Voltage(V)

  • P = I² x R

Power (W)= Current² x Resistance (Ω)

  • P = V² / R

Voltage² (V) / Resistance(Ω)

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5
Q

What is the Energy Equation

A

E = I x V x t

Energy (J) = Current(A) x Voltage(V) x Time (s)

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6
Q

What is always conserved in a DC (Direct Current) circuit

A

Charge and energy are always conserved

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7
Q

What are Kirchoff’s Laws and how do they show that charge and energy are always conserved

A
  • Kirchoff’s first law - the total current flowing into a junction is equal to the current flowing out of that junction. This shows that no charge is lost at any point in the circuit
  • Kirchoff’s second law - the sum of all the voltages in a series circuit is equal to the battery voltage. This shows that no energy is lost at any point in a circuit
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8
Q

What is Electromotive Force (e.m.f)

A

The amount of energy supplied by the source per unit charge

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9
Q

Electromotive Force Equations

A
  • E = E / Q

Electromotive Force (V) = Energy Supplied (J) / Charge (C)

  • E = I R + I r

Electromotive Force(V) = Current(A) x Resistance(Ω) + Current(A) x Internal Resistance(Ω)

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10
Q

What is load resistance

A

The total resistance of all the components in a circuit except the battery

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11
Q

What is internal resistance

A

The resistance of the materials within the battery or the limit of the flow of charge in the battery

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12
Q

What causes internal resistance

A

Internal Resistance caused by electrons colliding with atoms inside the battery, therefore some energy is lost before electrons even leave the battery

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13
Q

How is internal resistance represented in a circuit diagram

A

A small resistor inside the battery

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14
Q

What are the benefit of having a battery with low internal resistance

A
  • The battery can provide a higher currnet because internal resistance limits current
  • Less energy wasted in battery
  • Charges quicker as current is higher and less energy wasted
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15
Q

What is Terminal Potential Difference

A

The potential difference across the load resistance (R).

i.e. The energy transferred per unit charge flowing through the load resistance

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16
Q

What are Lost Volts

A

The potential difference across the internal resistance

i.e. the energy wasted by the cell per coulomb of charge

17
Q

What happens in a electromotive circuit when the load resistor decreases

A

The current will increase and the terminal potential difference will decrease

18
Q

Describe an experiment to calculate the e.m.f. and internal resistance of a cell

A
  • Connect the cell in series with an ammeter and variable resistor + connect a voltmeter across the cell
  • Vary the current using the variable resistor.
  • Record the voltage at each current
  • Plot a graph of voltage against current
  • y-intercept = electromotive force
  • Gradient = internal resistance
19
Q

Describe the Electromotive Force Circuit

A
20
Q

Describe and Explain the Terminal Potential Difference Graph

A
  • Y-intercept - Electromotive Force
  • X-intercept - The current when the cell is short circuited
  • Gradient - Internal Resistance
21
Q

Explain why terminal voltage decreases as current increase

A
  • As current increases the energy lost due to internal resistance would increase
  • and as current increases the lost volts increase
  • Therefore decreasing the terminal voltage
22
Q

When connecting a high-resistance voltmeter across a cell to find its electromotive what is the error in the results

A
  • Small amount of current flows through the voltmeter
  • So there are some lost volts
  • Measured value is very slightly less than the e.m.f.
  • But this is negligible
23
Q

Explain what is meant by a potential divider

A
  • A combination of resistors in series connected across a voltage source
  • To produce a required pd
24
Q

What is the purpose of a potential divider

A

To provide a constant specific potential difference

25
Q

How does the resistance of a light-dependent resistor vary

A

Resistance decreases as light intensity increases

26
Q

How does the resistance of a NTC thermistor vary

A

Resistance decreases as temperature increases

27
Q

Give a use of LDRs and thermistors

A

A light sensor or temperature sensor, so they can be included in circuits that control switches, e.g. to turn on a light or heating system

28
Q

Describe a method to see how the resistance across a thermistor varies with temperature

A
  • Place thermistor into water bath
  • Use a thermomter to measure the inital temperature
  • Measure the voltage and current at 10 degrees intervals from 0 - 100 degress using voltmeter and ammeter
  • Calculate resistance using R = V/I
  • Plot graph of Resistance against Temperature

physics paper 1 (15 decks)

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