Electricity Flashcards
Kirchhoff’s second law
In any circuit the sum of the electromotive force is equal to the sum of potential difference in a closed loop (conservation of energy)
Current in a series circuit…
In a series circuit, the current at every point will be the same
Current in a parallel circuit…
Current in each loop adds up to total current
P.d in a series circuit…
The emf will be split so total pd across each component is equal to the emf
P.d in a parallel circuit…
Pd across each loop is the same
Total resistance in series circuit…
The total resistance of a circuit containing resistors in series will be equal to the sum of resistance of each component
Rt = R1 + R2 + …
Total resistance in a parallel circuit…
Total resistance given by following formula
1/Rt = 1/R1 + 1/R2 + …
Where R1 and R2 are the total resistance values for each loop within a circuit
Internal resistance
Not all of the energy is transferred to the charge carriers is available to the circuit
E = I (R + r) —> E = V + Ir
With Y = I and X = V. What does a negative gradient represent
Internal resistance of cell
In electrical circuits what purpose do potential dividers serve
Alter resistance
Thermistor of LDR can be used to vary output of a potential divider
How do you calculate Vout
R2 / R1 + R2 x Vin
How does resistivity act
Acts as a constant to link resistance with area and length
P = RA / L
How does resistivity vary with temp
If resistance of material increases or decreases with changing temp, the value for resistivity will be affected in the same way
What is Ohm’s law
For a metallic conductor kept at constant temp the current is directly proportional to pd across it
How does Ohms law look on a graph
If it is obeyed there will be a constant linear gradient
