Module 4.3 Flashcards
Conservation of Energy
Energy cannot be created or destroyed - it can only be
transferred into different forms.
Internal Resistance
The resistance to the flow of charge within a source. Internal
resistance results in energy being dissipated within the source
Kirchhoff’s Second Law
A consequence of the conservation of energy. The sum
of the voltages in any closed loop must equal zero.
Lost Volts
The difference between a source’s emf and the terminal voltage. It is
equal to the potential difference across the source’s internal resistance.
Parallel Circuit
Components are said to be connected in parallel when they are
connected across each other (separate loops).
Potential Divider
A method of splitting a potential difference, by connecting two
resistors in series. The total potential difference is split in the ratio of their
resistances
Resistors in Parallel
The potential difference across resistors connected in
parallel is identical for each resistor. The current is split between the resistors. The
total resistance is equal to the inverse of the sum of the inverses of the
resistances of the resistors
Resistors in Series
The current through resistors connected in series is identical
for each resistor. The potential difference is split in the ratio of their resistances.
The total resistance is equal to the sum of the resistances of the resistors.
Sensor Circuits
A circuit that reacts to external conditions. They commonly
involve a semiconductor connected in a potential divider arrangement.
Series Circuit
Components are said to be connected in series when they are
connected end to end (in one loop).
Terminal PD
The potential difference across the terminals of a power source. It is
equal to the source’s emf minus any voltage drop over the source’s internal
resistance
How to determine internal resistance
To determine the internal resistance of a cell, the cell with internal resistance r is connected in
series to an ammeter and a variable resistor. A voltmeter is connected in parallel around the cell.
The resistance of the variable resistor is varied, and the V and I readings recorded. The equation 𝜀 = 𝑉 + 𝐼r is rearranged to 𝑉 = 𝜀 − 𝐼r. When a graph of terminal p.d. (V) against current (I) is
plotted, the y intercept of the graph will be the e.m.f. of the cell and the negative gradient will
be the internal resistance of the cell
what is constant in a series circuit
current
How to investigate potential divider circuits
A thermistor or LDR can be used to vary the output of a potential divider circuit (such as in
street lamps or air conditioning systems). When Vout is across a thermistor, a greater p.d. will be
provided when the temperature decreases, because this increases the resistance of the thermistor.
These circuits can be investigated using water baths and lamps to simulate different
environments, with a voltmeter across the desired component used to record the changes in Vout
as the environmental factors affecting the resistance of the component are varied.
What is the formula for Vout
Vout = (R2 / R1+R2) X Vin
Vout is the potential difference across R2
Vin is the e.m.f of the circuit
