Chapter 10: Electrical Circuits Flashcards
What is Kirchhoff’s Second law
For any path (loop) of a circuit, the sum of all the potential differences must equal the total emf of the circuit
How do you find the total resistance in a series circuit?
R1 + R2 + R3…
How do you find the total resistance in a parallel circuit?
1/R1 + 1/R2 + 1/R3…
Does adding a resistor to a circuit in parallel always reduce the total resistance?
Yes
How can you measure current in a circuit?
Ammeter connected in series to a component
How do you measure the potential difference of a component
voltmeter connected in parallel over the component being measured
In a parallel circuit, is the total voltage in each loop the same?
yes
How do you calculate the total voltage in a series circuit?
V1 + V2 + V3…
How does the current vary between each component of a series circuit?
current remains the same throughout the circuit
Is the current in each component of a parallel circuit the same?
No.
Each branch has a different current
Voltage across each branch is the same - the higher the resistance the lower the current flow
If two cells are connected in series, with positive terminal to positive terminal, what will be the total EMF?
ϵ1 + ϵ2
In a series circuit, if the cells are connected negative to negative, what would be the total emf be
ϵ1 - ϵ2
The EMFs would cancel out
Would the EMF of a source and its terminal voltage be the same?
No.
Not all the energy given to the charges in the course makes it out of the cell
Internal Resistance
the resistance within a power source due to the materials and components which make it up
What are ‘lost volts’
The difference in voltage between that supplied by the source and the amount available in the circuit.
They are ‘lost’ due to the internal resistance of the source
What is the equation relating e.m.f to total load and internal resistance
ϵ = I(R + r)
R = load resistance
r = internal resistance
ϵ = V + v
V = voltage used in circuit (terminal voltage)
v = lost volts
terminal voltage
voltage used in circuit after lost volts reduced from the e.m.f
Experiment to determine the internal resistance of a source
1) Set up circuit with a source, ammeter, voltmeter and variable resistor
2) Vary the resistance and measure V and I
3) Plot a V-I graph
4) V = -rI + ϵ -> V = mx +c
5) internal resistance = (-)gradient
What is the purpose of a potential divider?
To provide variable potential difference, or to provide a constant specific potential difference
How does the voltage across a component in a potential divider correspond to its resistance?
ratio of V to Vt = ratio of R to Rt
they are directly proportional
How can a potential divider circuit be used as a sensing circuit?
1) Put a resistor that varies with the desired conditions in a potential divider
2) Insert the responding load over either the variable resistor or fixed, depends on how circuit should work
How do you vary Voltage out in a potential divider circuit?
switch one of the resistors for a variable resistor
EMF Definiton
the energy per unit charge which is transferred from chemical to electrical energy
PD Definition
the energy per unit charge which is transferred from electrical to other forms
How to calculate the EMF of a circuit?
ϵ = I(R + r)
1) Measure terminal PD at different currents
Extrapolate the line back to the Y axis (terminal PD)
