PHY - 7. Current and voltage in circuits

what is potential difference

The amount of energy given to the charge in a circuit

what do you need for an electrical current to flow (2 things)

• A material that allows electrical charge to pass through it, conductors

• An energy source to push the electrons along, battery/ cell

why are metals the best conductors

closely-packed atoms and they have delocalised electrons that are free to move throughout the metal

what are conventional currents

the flow of electrical charge, it measures how many electrical charges are passing each second

how do electrons actually flow (conventional current)

negative to positive

how do conventional currents flow

positive to negative, need to know this for exams

current equation

I = Q/t

current = charge / time

unit of current

amps, A

unit of charge

coulombs, C

voltage equation

V = E/Q

voltage = energy/ charge

energy unit

Joules, J

open switch symbol and definition

breaks the circuit so current can’t flow

closed switch symbol and definition

Completes the circuit so current can flow

battery vs cell

cell - provides potential difference/ voltage

battery - a collection of cells

diode symbol and definition

allows current to flow in one direction

fixed resistor symbol and definition

increases resistance in circuit

variable resistor symbol and definitions

can vary potential difference of a circuit by varying resistance

bulb symbol and definition

produces light

fuse symbol and definition

If current is too high the fuse melts breaking the circuit and preventing current from flowing

voltmeter definition

measures voltage

ammeter definition

measures current

thermistor symbol and definition

As temp. increases it decreases resistance

L.D.R symbol and definition

As light intensity increases it decreases resistance

Series Vs Parallel

A series circuit is a circuit with just one loop while a parallel is a circuit with more than one loop

Rule for current in a series circuit

Current is always the same anywhere in the circuit

Resistance in a series

The sum of all resistors in the circuit

Rule for voltage in a series circuit

Voltage splits between components

How does a voltmeter always have to connect

In a parallel circuit, hugs the component

Rule for current in a parallel circuit and why

Current is split amongst the components

current splits because the electrons travel down different branches, that reduces the number of electrons on each branch

Resistance in a parallel circuit

The sum of resistors is less than the resistance of the smallest resistor

R_T = 1

. ——————————

. ( 1/R₁ + 1/R₂ + … 1/R_n )

rules for voltage in a parallel circuit

Voltage is the same in each branch of the circuit