electric circuits electric current the amount of charge passing through a surface per second....
TRANSCRIPT
Electric CircuitsElectric Circuits Electric Current
The amount of charge passing through a surface per second.
• Unit: ampere or amp (A) = coulombs/seconds
The “conventional” current (I) is defined by the motion of positive charges → Benjamin Franklin
04/20/2304/20/23 APHY101APHY101 11
Electric CircuitsElectric Circuits Drift Speed
The average speed of charges that make a current
• Usually ~ 0.1 mm/s
The electric field is created throughout the wire so that all charges respond almost instantaneously
The charges collide with atoms in the wire and proceed with a random walk
• The atoms get hotter due to these collisions → light !
04/20/2304/20/23 APHY101APHY101 22
Electric CircuitsElectric Circuits Ohm’s Law and Resistance
• Unit: ohms (Ω) = volts/amps
04/20/2304/20/23 APHY101APHY101 33
Electric CircuitsElectric Circuits Resistivity
What determines the value of R for a resistor?
• Type of material, length and thickness• Temperature?
Conductors, insulators, heating units, lights, etc.
04/20/2304/20/23 APHY101APHY101 44
Electric CircuitsElectric Circuits
04/20/2304/20/23 APHY101APHY101 55
Electric CircuitsElectric Circuits Energy and Electric Potential in a Circuit
The PE of a charge is unchanged after traveling around a circuit
PE is gained at the voltage source (ie. battery) and lost at the resistor (ie. light bulb)
The sum of the ΔV around the circuit equals zero
• Voltage “drops” across a resistor04/20/2304/20/23 APHY101APHY101 66
Electric CircuitsElectric Circuits Series circuits
04/20/2304/20/23 APHY101APHY101 77
Electric CircuitsElectric Circuits Series circuits
1. The current is the same everywhere in the circuit.
Itotal = I1 = I2 = …
2. The total resistance of the circuit isRtotal = R1 + R2 + …
3. The sum of the voltages across each device equals the source voltage
ΔVsource = ΔV1 + ΔV2 + …
04/20/2304/20/23 APHY101APHY101 88
Electric CircuitsElectric Circuits Parallel circuits
04/20/2304/20/23 APHY101APHY101 99
Electric CircuitsElectric Circuits Parallel circuits
1. The total current in the circuit equals the sum of the current in each device.
Itotal = I1 + I2 + …
2. The total resistance of the circuit is
3. The voltage across each device is the same.
ΔVsource = ΔV1 = ΔV2 = …04/20/2304/20/23 APHY101APHY101 1010
Electric CircuitsElectric Circuits Electric Power
Energy transfer per unit time• Unit: watts or joules/second
Since it takes work (W) to move a charge (q) through a potential difference (ΔV) then we can say that
04/20/2304/20/23 APHY101APHY101 1111
Electric CircuitsElectric Circuits Electric Power
Overloading occurs when the circuit resistance drops to where the circuit carries too much current.
Fuses or breakers are used to control the amount of current in a circuit
04/20/2304/20/23 APHY101APHY101 1212