Source of electromotive force

device that transforms one type of energy → electric energy (ie. battery)

EMF (ℰ) of the source:

potential diff (V) between terminals of device when no current flows to an external circuit

Is a battery a source of constant voltage or current?

Voltage

Internal Resistance (r)

opposition to the flow of current (I) from the cells/ batteries themselves

resulting in the generation of **heat**

When is internal resistance more relevant?

With GREATER external resistance

Terminal voltage

potential diff (V) across the terminals of a battery when the circuit is switched on

V_{ab} = V_{a} - V_{b}

What is terminal voltage when **no current** is drawn from a battery?

terminal voltage = emf

What is terminal voltage when current flows from a battery? EQUATION

Circuit in **series**

connected end to end along a single path

**Resistors** in SERIES

- Charge has only
**1 path to flow**(current through each resistor same) - Charge loses energy as it passes through each resistor (voltage drop)
- Sum of each voltage drop (V) = voltage of battery.

total resistance > individual resistance

**Resistors** in PARALLEL

- Charge has multiple paths to flow.
- Voltage across each resistor = voltage of battery.

total resistance < individual resistance

**Capacitors** in SERIES

Net effect: LOWER capacitance

**Capacitors** in PARALLEL

Net effect: HIGHER capacitance

(essentially increasing area of the plates where charge can accumulate)

Kirchoff’s Junction Rule

sum of all currents entering the junction = sum of all currents leaving the junction

Kirchoff’s Loop Rule

sum of the changes in potential around any closed loop of a circuit = 0

V = 0

When 2+ sources of EMF are arranged in series (normally)

V_{eq} = V_{1} + V_{2} + … + V_{n}

When 2+ sources of EMF are arranged in series (opposite)

V_{eq} = V_{1} – V_{2} – … – V_{n}

Electrons are forced into – terminal and removed from + terminal

Only works for rechargeable batteries (otherwise waste of energy)

What are the pros of arranging batteries in parallel?

Battery will go dead less quickly

Can provide **more energy** when more current is needed

Energy loss due to **internal resistance LOWER** (b/c each cell has to produce only a fraction of the current)

Electric current through the human body can cause damage in 2 ways:

- Heating tissue & causing burns
- Stimulating nerves & muscles (shock)

**Ammeter**

measure current (series)

Ideally 0 internal resistance

**Voltmeter**

measure voltage (parallel)

Ideally HIGH internal resistance to DECREASE current

**Multimeter**

measure voltage, current, resistance

**Ohmmeter**

measure resistance (must contain battery of known resistance)

__Capacitor in circuit with no battery__

Initially charged and now DISCHARGING

__Capacitor in circuit with no battery__

Initially uncharged, now CHARGING