P4

What is a conductor

A material where electrons can flow - they are delocalised

What is an insulator

A material where electrons cannot flow - they are in fixed position

Why do electrons transfer when insulators are rubbed together?

Because of friction, the electrons are outside the nucleus and weakly bound to their atoms

Steps that cause a spark

separation of charges --> potential difference, high enough pd --> charge moves --> spark

Resistor circuit symbol

--[ ]--

Ammeter circuit symbol

---(A)---

Lamp circuit symbol

---(X)---

Cell circuit symbol

---|I--- (positive end left)

Battery circuit symbol

---|I---|I--- (2 or more cells - positive end left)

Where do electron flow from and to in a circuit?

negative --> positive port

What is current + measured in?

the rate of flow of charge, measured in Amps (A)

Formula for current

current (I) = charge (Q) / time (t)

What is charge measured in?

Coulombs (C)

What is time measured in (for current)

seconds (s)

What is potential difference?

Energy transferred per coulomb of charge (to an object when each couloumb passes through), no. of joules of work done per coulomb of charge to make current flow

What is the formula for potential difference? energy t

energy transferred / charge

High resistance = ?

low current and vice versa

What is resistance?

The measure of how much the current flow is restricted in a circuit

Which components in a circuit have resistance?

All of them!

Formula for resistance?

Resistance = p.d. / current

As p.d. increases?

The current also increases

What is Ohms Law?

That p.d. is directly proportional to current (if temp. is constant)

Formula for potential difference? I

p.d. = current x resistance

What is a series circuit?

Components in a single loop

What is a current like in a series circuit?

It is the same all over the circuit

What is the p.d. like in a series circuit?

It is shared across the components

How to calculate total resistance in series circuit?

The sum of the resistance of all components in a series circuit

Resistance is ... to current

Resistance is inversely proportional to current E.g. increase resistance by 2 times, current decreased by 2 times

Current in parallel circuits

Total current is split between branches - current flow through branches aren't as strong as put together

P.d. parallel circuits

components in parallel - p.d. across each component is the same

Total resistance formula

= battery p.d. / total current entering the combination

How will adding loops effect the resistance?

It will lower the overall resistance of the circuit (current increases so resistance decreases)

total resistance in parallel circuits?

Total resistance always less than loop with lowest resistance

Describe a short circuit

There is a branch with negligible resistance in a regular wire - current flows through regular wire loop and not through the branch with the bulb --> bulb doesn't light

Describe a current-p.d. graph - filament lamp

Line curves away from y-axis - current not directly proportional to p.d. - p.d. decreases - S SHAPE, resistance increases as filament lamp's temp. increases

Describe a current-p.d. graph - diode

Line flat then suddenly curves towards y-axis - current not directly proportional to p.d.

What is a non-ohmic conductor?

When the current is not directly proportional to p.d. when going through a counductor

Describe a diode

Current flows through in 1 direction, diode's resistance in reversed direction a lot higher than resistance in forward direction --> reversed direction current virtually 0

What is a thermistor?

A temperature resistor - resistance decreases if its temp. increases (+ vice versa)

Light Dependent Resistor component symbol

---(-[ ]-)--- With arrows pointing in

Describe a LDR

Light dependent resistor, light intensity increases --> resistance decreases --> current through LDR increases

How do daylight adjusting lights work?

If sunny: light intensity high, resistance very low, loop with LDR has lowest resistance, most current flows through LDR (not through lamp so lamp doesn't emit light). Opposite when dark

Describe static shock - sparks

distance between 2 charged objects decreases, force between them increases. As the force is stronger, it draws the electrons in air molecules, meaning the air has a positive charge. Leads to a stream of electrons to flow from neg. charged object to pos. charged object. This causes the air to get so hot it glows white = spark