physics unit electricity

static electricity

the buildup of an electric charge on the surface of an object. It occurs when negatively charged particles (electrons) transfer from one material to another,

current electricity

movement of charges

alternating current

current that changes direction

direct current

current that does not change direction

voltage

supplies the energy source that allows charges to move

potential difference

the energy available for charges to move

current

movement of charges in a period of time

amps

– unit of current

resistance

impedance to current flow

equivevalent resistance

total resistance in a circuit

ohms

unit for resistance

power

energy per time

watt

unit of power

ohms law

V = IR; relationship between voltage, current, and resistance

open circuit

circuit that does not make a complete path

series circuit

circuit in which current must flow through all components

parallel circuit

circuit in which there are branches

combination circuits

composed of both parallel and series circuit components

volt meter

device used to measure voltage; placed in parallel

anmeter

device used to measure current; placed in series

resistor

– component that slows down current

fuse

- a safety device consisting of a strip of wire that melts and breaks an electric circuit if the current exceeds a safe level.

circuit breaker

- an automatic device for stopping the flow of current in an electric circuit as a safety measure.

equation for power

p=iv

What’s the difference between static electricity and current electricity?

Current electricity: moving charge/electrons

Static electricity: stationary charges (charges transfer and then remain still)

unit for charge, work, voltage, current, resistance, and power

Charge: Q or q Coulombs (C)

Work: W Joules (J)

Voltage: V Volts (V)

Current: I (capital i) Amperes (Amps or A)

Resistance : R Ohms (Ω)

Power: P Watts (W)

difference between voltage and current

Current is the flow of electrons per unit time. Voltage is the potential energy difference that drives/pushes the flow of electrons.

Will a light bulb which requires 60 W of power be brighter or dimmer than a light bulb which requires 75 W of power?

• dimmer

• more power = brighter lightbulb

If the lights in a room are switched off, is the circuit containing the lights open or closed?

open

What is constant for resistors connected in series? What is summed?

• current is constant

• voltage, resistance, and power are summed

What is constant for resistors connected in parallel? What is summed

voltage is constant; current and power are summed

summed in a circuit

multiple electrical quantities (such as currents or voltages) are combined together to produce a single cumulative output.

What does a voltmeter measure and how is it inserted into a circuit?

• voltmeter measures voltage drop

• placed in parallel

What does an ammeter measure and how is it inserted into a circuit?

• ammeter measures current

• placed in series

Is the total resistance larger or smaller than the individual resistances when resistors are connected in series? Parallel?

• total resistance increases when resistors are connect in series

• total resistance decreases when resistors are placed in parallel

If 7 Ω, 4 Ω, and 2 Ω resistors are connected in series, which resistor draws the most current? If these resistors

are connected in parallel, which resistor draws the most current?

• in series all three resistors draw the same amount of current

• in parallel the 2 Ω draws the most current

What happens to the brightness of a light bulb if another bulb is connected to it in series? Parallel?

• in series, the brightness will decrease as more light bulbs are added

• in parallel, nothing happens

Two light bulbs are connected in the same circuit. What happens if the filament of one bulb breaks when the bulbs are connect in series? Parallel?

• Series: circuit is open, no current flows

• Parallel: only the branch with the broken lightbulb is open, current will not flow through that branch, but current will still flow through the other branches

series circuit examples

• christmas lights

• battery banks

• when one bulb goes out, they all go out

parallel circuit examples

• two or more paths for current to flow, meaning components are connected side-by-side

• car headlights

• household lights

purpose of a fuse

a fuse is a safety feature – when current flows to quickly the wire inside the fuse will melt, stopping the circuit

altrernating vs direct current

direct current flows continuously in one direction, alternating current changes direction constantly