- Same everywhere - Only one way electrons can flow

- Added together - One electron flow so all encounter same resistance

- Different - They choose path of least resistance

- Different, cannot add - 1/R1 + 1/R2 + 1/R3 -Cuase not all resistance is in the same route

Topic 10- Electricity and Circuits Flashcards by Artemis Buxton

What is potential difference?

Energy transferred per charge
Electrical energy carried by electrons
Diference of potential electrical between two points
How much (energy) is used in a component

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What is current?

-Flow of electrons
- From positive to negetive…

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What is a volt in coulombs?

Joule/coulomb
- potential difference is how much energy transfered per unit of charge/ current

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Charge =

I,t

Current x time

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Energy =

Q, V

charge x potential difference

number of electrons x how much energy transferred to components

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Why does potential difference cuase flow of electrons

-creates an electric field that
-exerts a force on the negatively charged electrons
-causing them to flow

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where is current conserved?

current is conserved at a junction in a circuit

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How does a variable resistor work?

Lengthens wire and increases resistance
Decreases current

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Voltage =

R,I

Resistance x Current

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What is current measured in?

-I
-Amps

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What is Voltage measured in?

-V
-Volts

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What is charge measured in?

-Q
-Coulumbs

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What is energy measured in?

-J
-Joules

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What is resistance measured in?

-Ω
-Ohms

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Potential difference series?

Split
All components only have enough energy as batterty

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Current series?

Same everywhere
Only one way electrons can flow

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Resistance series?

Added together
One electron flow so all encounter same resistance

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Potential difference parallel?

-Same everywhere
- Current and resistance are indirectly proportional, keeping voltage the same

-choose path of least resistance
-But more electron flow cuases higher resitance
-so overall less r and more I
-or more r and less I
-V= IR

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Current parallel?

Different
They choose path of least resistance

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Resistance parallel?

Different, cannot add
1/R1 + 1/R2 + 1/R3

-Cuase not all resistance is in the same route

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Why does net resistance decrease in parallel?

Adding another pathway for electrons
(3 resistors in series vs 3 resistors in parallel)
(electrons go through all 3 vs just one per route)

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Core Practical: Construct electrical circuits to:

a) investigate the relationship between potential difference, current and resistance for a resistor and a filament lamp

1) Variable resistor: changes voltage by changing resistance

2)Ammeter: Take readings of current

3)Volmeter: Take reading of voltage across the fixed resistor

4) Fixed resistor: Investigate how higher volt supply changes current if resistance does not change

Independant: Voltage (variable resistor)
Dependant: Current
Control: Same components/fixed resistor and power supply

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Core Practical: Construct electrical circuits to:
test series and parallel circuits using resistors and filament
lamps
RESULTS

-Attach 2 lamps in series with ammeter and volmeter (around both lamps)
-Take readings
-Repeat in parallel circuit

-Brighter in parallel as there are more routes for electrons and therefore less resistance

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How does current vary with potential difference for a filiment lamp
relating to its resistance?

Describe graph and explain

slight S shape
When more V is supplied it is brighter and hotter
Heating effect cuases more resistance meaning less current

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How does current vary with potential difference for a **diodes** relating to its resistance?

- Flat line and sudden rapid increase at 0.6-0.7 v -As Voltage increase -Resistance decreases rapidly -Causing current to rapidly increase

How does current vary with potential difference for a **fixed resistors** relating to its resistance?

- Directly proportional - Resistance is fixed

What is an ohmic conductor?

Current and voltage are directly proportional if temperature is constant

How does resistance change with brightness of an LDR

- Higher resistance when dimmer - Lower resistance when brighter

How does resistance change with temperature of an thermister

- Higher resistance when coldere - Lower resistance when hotter

Experiment to find relationship witth volts and current of a **resistor or filiment lamp**:

-Battery: supply potential difference -Ammeter: current -Volmeter: across the resistor/ lamp 1) Note down readings 2) Variable resistor: changes resistence and therefore voltage 3) Reverse battery/ current for negative readings

Experiment to find relationship with volts and current of a **resistor**: **PROBLEM** and **SOLUTION**

- Get too hot/heating effect increase resistance - Don't leave circuit on for too long

Why do we use a fixed resistor in a circuit with a diode?

- Diodes easily damaged by high current - extra resitor keeps current reletively low

What and why do we use instead of an ammeter for **diode** experiment?

- Miliammater (reads smaller currents) - Low current (extra reistor)

Experiment to find relationship witth volts and current of a **Diode**: | Same as + what is extra

- Same as resistor/ filiment lamp - Use extra resistor and a miliammeter - there will be no readings for reveresed current

What is the heating effect?

Resistance cuases electrons to transfer energy in the form of heat

How to reduce energy loss in circuits?

- Low resistance wires - Insulate wires

Why do hotter wires cuase higher reistance?

-Ions vibrate more -More likely to collide with electrons

Heating effect posisitves/ Uses?

-Kettle -Domestic heating -Electric ovens/ toasters | electrical work ---> thormal store

Heating effect disadvantages?

- Energy loss - Fire hazard

Energy = | current

Current x Time x Potential difference | E= I x t x V

What is power

Rate of energy | Energy transferred per second

Power=

Energy/ Time | P = E/T

Power = | Current

Current x Potential difference | P = IV

Power = | power loss due to resistance

Current ^2 x resistance | P= I^2 x R

Direct vs Alternating current: voltage

-Direct: voltage remains the same -Alternating: Voltage switches between positive and negative

What supplies + what is direct current?

- Battery/ Cell - Current moves in one direction only

What is an alternating current?

- Charge movement changes direction

Uk domestic supply: Curent, Hz and voltage

- a.c (alternating) - 50Hz (alternates per second) - 230 V

What does the live wire do?

- Supplies alternating potential difference of about 230 volts

Live wire colour?

Brown

Neutral wire colour?

Blue

Earth wire colour?

Green and yellow striped

What does the neutral wire do?

- Completes the circuit - Carries away current (out/ back into mains)

Earth wire and Neutral wire potential difference

0 volts

What does the Earth wire do?

- Stops the casing from becoming live - By allowing an alternate pathway for the current to flow

What are wires made of?

-Copper

Why should a fuse and switch be attached to the live wire?

- To break the connection to the mains supply (fuse melts due to too much current heating it up, as it has a low melting point) - Stop the casing becoming 'live'

Why is the earth pin longer?

-Connects with the socket first -Provides alternative pathway incase live wire is broken

What would happen if the live and Earth wire touched?

- Direct circuit between the Earth and 230v - Could cause a fire or shock

Which domestic electrical appliances have higher power ratings?

Thermal apliances (kettle/oven vs fan)

What do power ratings show?

Energy it transfers/ work done per second