Electric Current

potential difference
the difference in electrical potential between two points, measured in volts. When two point of different electric potential are connected by a conductor, charge flows so long as a potential difference exists.
electric current
the flow of electrical charge that transports energy from one place to another. Measured in amperes (aka "amps"), where 1 A is the flow of 6.25 x 10¹⁸ electrons per second, or 1 coulomb per second I= V/R
electrical resistance
the property of a material that resists electric current. Measured in ohms (Ω) V/I = R
Ohm's Law
the current in a circuit varies in direct proportion to the potential difference or voltage across the circuit and inversely with the circuit's resistance
Current = voltage/resistance
(a potential difference of 1 V across the resistance of 1 Ω produces a current of 1 A)
direct current (dc)
electrically charged particles flowing in one direction only
alternating current (ac)
electrically charged particles that repeatedly reverse direction, vibrating about relatively fixed positions In the United states, the vibrational rate is commonly 60 Hz
electric power
the rate of energy transfer, or rate of doing work; the amount of energy per unit time, which electrically can be measured by the product of current and voltage.
Power = current x voltage
(Electric power is measured in watts (or kilowatts), where 1 W = 1A x 1V = 1 J/s
parallel circuit
an electric circuit in which electrical devices are connected in such a way that the same voltage acts across each one, and any single one completes the circuit independently of all of the others
series circuit
an electric circuit in which electrical devices are connected along a single wire such that the same electric current exists in all of them
For current to flow, you need a ____ and a ____.
(What causes what?) _____ causes _____ (Evidence _______).
It's the amount of _______ that hurts or kills you, not the ________.
For current flow, you need a voltage source and a complete circuit. Voltage causes current ( evidence: battery example).
It's the amount of current that hurts or kills you, not the voltage.
For SERIES circuits...
______ is the same throughout. _____ adds (meaning total ___ = the sum of ____).
When you add more light bulbs in series, the brightness _____. ) REQ= ________.
When you add more batteries in series, bulbs ____. (b/c an increase in ___ causes an increase in ____).
For SERIES circuits...
current stays the same throughout. Voltage adds (meaning Vt = Va+Vb). When you add more light bulbs in series, the brightness decreases.) REQ = R1 +R2 .
When you add more batteries in series, the bulbs increase brightness. (b/c an increase in voltage causes an increase in current).
For PARALLEL circuits...
_____ is the same throughout. _____ adds (meaning total ___ = the sum of ____).
When you add more light bulbs in parallel, the brightness _____. REQ= ________.
When you add more batteries in parallel, bulb brightness _____. (b/c they are _____)
For PARALLEL circuits...
voltage stays the same throughout. current adds (meaning total current = the sum of Ia+Ib). When you add more light bulbs in parallel, the brightness remains the same. REQ=(R1 x R2)/(R1+R2). When you add more batteries in parallel, the bulb brightness remains the same. (b/c they are separate circuits).
definition, symbol, formula, and units of voltage
voltage is electric potential energy per unit charge and is measured in volts (V). V=IR.
definition, symbol, formula, and units of power
power is the amount of work done per unit time. (P= J/S) power is measured in watts (w). P = IV.
current through, voltage across, voltage drop, energy used, power consumed
what does a battery do? how does it do it? What does the "12 Volts" mean on your car battery?
the battery creates a constant voltage source because the positive charge flows from the positive terminal (through a circuit) to the negative terminal
What are two analogies for Current/Voltage/Battery?
1. water analogy: the flowing water is the flowing charge (aka electric current). the water pressure is the voltage, and the water wants to flow from high pressure to low pressure, and the pump is the voltage source, which pushes the water up to high pressure.
2. the battery creates an "electric hill", and positive charges flow down the "hill", which is current.
Are car headlights wired in parallel or series? What's your evidence?
headlights are wired in parallel so that the rest of the lights will remain working, even if one of them is broken.
Which is better for electricity transmission: AC or DC? Why?
Ac is better for electricity transmission because it's easier to change AC to higher and lower voltages (aka "stepping up" or "stepping down"), and higher voltage leads to lower energy losses over long distances (from power plants to houses). Wall outlets use AC (60 Hz) and batteries use DC.
What's a dangerous level of current?
Why is that an easier question that "What is a dangerous level of voltage?"
A dangerous level of current depends on the body's resistance. When you are dry, your resistance is 500,000Ω when you are wet, your resistance is 100Ω. .070 is dangerous to a human.
Why is there a 3rd hole/prong on wall outlets?
the 3rd wire is attached to the outside metal of an appliance. If a "live" wire touches the outside metal, then the current goes directly to the ground, and not through you.
How does the speed of these 3 things compare?
1. electrons moving in non-conducting wire 2. electrons traveling down a conducting wire 3. the speed of the light turning on (when you flip the switch). Explain the differences.
1. electron sin a non-conducting wire are moving in random directions at a million kilometers per hour, but there's no net current.
2. when electrons travel down a conducting wire, the nudged electrons collide with the wire atoms and electrons, so they move through the wire very slowly (this is called the drift velocity because the electrons only move one meter every 3 hours).
3. when you flip on the switch, electrons continue in their random directions, but the potential difference causes a slight net nudge of each electron. the field travels through the wire at close to the speed of light.
Baghdad battery
a really old battery made of a clay jar that produces 1.1 volts.
Galvani experimented with the frog legs, thinking he had found the "life force"
frog legs
frog legs contracted when static electricity passed through them
circuit breakers
circuit breakers trip when there is too much current
fuses melt when there is too much current so that the appliance does not catch on fire
birds on telephone wires
there is no direct electric path to the ground