# Physics Year 11

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Physics Year 11
Electrical Circuits

Voltmeters & Ammeters
• Voltmeter –measures PD between 2 points • Connected in parallel to the component it is
measuring the PD across • High resistance instruments (little I diverted) • Ammeter measures I at a point • Connected in series • Very low resistance (little effect on I) • Polarities – right way round

Series Circuits
• Resistors connected end to end = series • Resistors connected in series V is shared
among resistors • V = 𝑉1 + 𝑉2 + 𝑉3 • Same I goes through all • Total resistance is the sum of the individuals

Worked Example

Disadvantages of Series Circuits
• Series circuits have two disadvantages when compared with parallel circuits.
• The first disadvantage is that, if one component in a series circuit fails, then all the components in the circuit fail because the circuit has been broken.
• The second disadvantage is that the more components there are in a series circuit, the greater the circuit's resistance.

Parallel Circuits
• In parallel means placing it by the side of another • If 𝑅1 is connected as
• Then amount of I flowing in the circuit increases • Reason = 𝑅2 allows I to flow in another pathway • I is shared among resistors • Same V across each • Total resistance is less than

Parallel Circuits continued
• 3 ohmn resistor & 6 V cell • I flowing = 6/3 = 2A
• Another resistor of 6 ohmns • Forms separate circuit • I = 6/6 = 1A • Total I flowing from cell =2+1A • Total R= V/I = 6/3 = 2 ohmns

Rules for a Parallel Circuit.
• Current in a Parallel Circuit.
• The current in a parallel circuit depends on the resistance of the branch.
• The total current flowing in to the branches is equal to the total current flowing out of the branches.
• A1 = A5

Current in a Parallel Circuit.
• The current at A2 flowing through the 2 Ohm resistor can be found using V = I x R
• If the supply voltage is 12 Volts, • I=V/R • = 12 / 2 • = 6 Amps.

Parallel Notes
• For parallel circuits, each component behaves as if it is connected independently to the cell, and is unaware of the other components
• If an identical cell (battery) is placed in parallel with the original cell the current stays the same because the total voltage of the circuit is the same.
• The two cells together provide electricity for twice as long before they both run out.

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