Chapter 10, Electrical Circuits Flashcards
What is Kirchhoff’s second law?
The sum of the E.M.F. is equal to the sum of the P.D.’s in a closed loop (i.e. the total energy provided in a circuit is equal to that leaving it).
In a circuit where a battery with E.M.F. of 3 E provides for two resistors of resistance 2 R and 1 R then what is the P.D. of each resistor?
The 2 R resistor will use 2 E and the 1 R resistor will use 1 E.
If 2 cells of E.M.F. e are facing opposite directions in a circuit what is the total E.M.F.?
0.
How do you find the total resistance of resistors in series?
Add the resistance’s together (this can be derived from Kirchhoff’s second law as the total P.D. = IR1 + IR2 + … = IR)
How do you find the total resistance of resistors in parallel?
Add the inverse of all the resistance’s and find the inverse of the result.
What is internal resistance?
The resistance of the battery/cell used.
What is the name for the difference in terminal P.D. and the E.M.F. of a cell?
Lost volts.
How do you find the lost volts and therefore E.M.F. of a cell?
Measure the current and use V=IR, ε = I(R+r) where r is the internal resistance and R is the resistance of the circuit.
By taking a variable resistor the current in a circuit can be changed allowing you to plot a graph of V against I to find the E.M.F. of a cell. How is this information obtained from the graph?
The y intercept (V axis) is the ε, the gradient is -r.
How can potential divider circuits be used to make sensors?
By having a variable resistor which is dependant on the variable you are measuring (e.g. use a thermistor to measure temperature) and measuring the change in V out
What is a potentiometer?
A resistor (usually coiled wire) where a contact can be slid across it to create a potential divider where R1 is dependant on the distance from the input to the contact and R2 is dependant on the remaining length. Sometimes these use a dial rather than slider.
