Electric circuits Flashcards
Ohmic conductor
and obvious opposites of non-ohmic conductors
Conductor with resistance that is constant for a wide range of :
-voltages
-currents
and obeys ohms law
Voltage
and unit analysis
Difference in electric potential energy per unit charge measured across two points
V = J.C-1
V=W/Q
Current
Measure of electric charge passing through a conducting material/point per unit time
A = J.C-1
I = Q/t
Emf
Electric potential difference between terminals of a battery when NO current is flowing.
OR
Energy per unit charge needed to move an electron from + to - terminal of the battery
V= J.C-1
Resistance
obstacle to the flow of charge
- Ration of voltage over current strength
1 ohm = 1 V.A-1
Ohm’s law
The potential difference across a conductor is directly proportional to the current in the conductor at constant temperature.
Power
The rat eat which work is doen ( P = W/t)
The rate at which electrical energy is transformed /converted into other forms of energy
W = J.s-1
Voltage and current in series and parallel circuits
Series: Current =, voltage /
Parallel: Current /. voltage =
Note on energy given per electron through the circuit in relation to resistors’ effects
Every Coulomb that goes through the circuit loses the same # energy.
Different resistors limit the amount of coulombs NOT THE ENERGY PER COULOMB (thus resistor affect current not voltage as V = W/Q)
Internal resistance
The resistance inside a cell due to the loss of electric potential energy per coulomb as charge leaves/enters the cell
4 factors affecting r
- Size of cell
- Chemical properties
- Age
- Temperature
- Current of the battery
Terminal potential difference (Vload)
Potential difference across the terminals of a battery when there IS A CURRENT flowing in the circuit
Vload = IRext
Lost Volts
The difference between the emf and the terminal potential difference
Emf = Vint + Vload
Vint + Vext
Short circuit and 2 consequences
A path of very low resistance
What happens?
R tends to zero and I tends towards Imax
Consequences:
- The wire heats up rapidly
- the cell goes flat very quickly
Faraday’s Law
The magnitude of the emf induced in a coil is proportional to the rate of change of magnetic flux
Emf = -N Phi/delta t
Why is a current induced in a wire coil when it is rotated in a magnetic field.
The coil has a fixed surface area. The number of field lines through the surface changes as the coil rotates so the flux changes over time. The change in flux induces an emf. If the coil is part of closed circuit then the current flows.
Rms
Rms value of ac is the DC potential difference or current which dissipates the same amount if energy as ac
