Electricity RevisionNotes p.1

Current = charge transferred per second

I = Q / t

Potential Difference = difference in energy per coulomb of charge between 2 points in a circuit.

Symbols

Quantities – Symbols – Units – Unit Symbols

Circuit Rules

Series Circuits

Parallel Circuits

Current & Voltage

Current and Voltage

Current and Voltage

Current and Voltage

-+

How many paths from – to + ?Only 1 … so what type of circuit is it?

A series circuit!

Voltage in Series

-+Vs

V1 V2

•Voltage is a measure of the energy carried by the charges in a circuit.•Voltage is measured in Volts (V)•We use a voltmeter to measure voltage. V

Voltage in Series

•1 lead to COM, 1 lead to V . Dial to 20 V.•DO NOT break the circuit.•Connect voltmeter “on top of” components.

Vs

V2V1

Eg)

Current in Series

-+

A

AA

A

•Current is a measure of how quickly the charges move around the circuit.•It is measured in Amperes (A)…”amps”•We use an ammeter to measure current. A

More Revision of Circuits (not in notes)

200 100

100

A2

A1

12 V+ -

R

Y

P

X(0J) Q

(8J) (12J)

(12J)(0J)

1. Supply Voltage (12V) is a measure of how much “electrical potential”energy each coulomb of charge gains as it passes through the supply.

In the circuit above each Coulomb gains 12 J of energy. i.e.12 V = 12 Joules per Coulomb (J/C)

1. Supply Voltage (12V) is a measure of how much “electrical potential”energy each coulomb of charge gains as it passes through the supply.

In the circuit above each Coulomb gains 12 J of energy. i.e.12 V = 12 Joules per Coulomb (J/C)

2. Voltage (or potential difference) across a component: This tells us how much energy each coulomb “loses” in the circuit’s components. (Thisenergy is not really “lost”, it is transformede.g. to heat in the resistor!e.g. to light and heat in a bulb!

In the circuit• At R – each coulomb has 12 J or energy.• At Y – each coulomb has 12 J or energy.• At Q – each coulomb has 8 J or energy (as 4 J were used in the 100

resistor, 8 J used in the 200 resistor).• At P – each coulomb has 0 J or energy.• At X – each coulomb has 0 J or energy.

Then• voltage across QR = p.d. across QR = 4 V (or 4 J/C)• voltage across QP = p.d. across QP = 8 V (or 8 J/C)• voltage across XY = p.d. across XY= 12 V (or 12 J/C)

Then•voltage across QR = p.d. across QR = 4 V (or 4 J/C)•voltage across QP = p.d. across QP = 8 V (or 8 J/C)•voltage across XY = p.d. across XY= 12 V (or 12 J/C)

3. Current is a measure of the amount of charge, Q, measured in Coulombs, which passes a point per second.

Reminders I = Q t

I = V R

NB ALWAYS CONSIDER WHICH RESISTORS AND VOLTAGES (p.d.’s)AFFECT THE CURRENT AT ANY POINT FOR CALCULATIONS.

e.g. At A1 – supply voltage + total resistance of the circuit.

1/RT = 1/R1 + 1/R2 = 1 + 1 100 300 RT = 75

RT = 75 VT = 12 VI = ?

I = V R = 12 75 = 0.16 A

I = V R = 12 300 = 0.04 A

e.g. at A2 – Voltage across PR + resistance at PR need to be used.

RT = 300 VT = 12 VI = ?

Problems on CIRCUITS REVISION A - D.

Revision of CircuitsUse the Standard Grade Physics books to remind yourself of how to find a) resistance in parallel.

b) voltage across a voltage divider circuit.

c) the value of the resistor in series with an LED.

1/RT = 1/R1 + 1/R2

V1 = R1 x VS (R1 + R2)

V1 = R1 V2 R2

VR = VS – VLED

THEN……… R = VR

I

Problems 5 – 20on page 55 of the Problem booklet.