AS Physics Unit 1.11 Internal Resistance And E.M.F Flashcards
What are some forces of E.M.F?
Batteries and power packs.
What is internal resistance?
It is the resistance to the electric current that passes through sources of E.M.F?
What is one of the two effects internal resistance has on a source of E.M.F?
When more current is drawn from the battery or power pack, the voltage across the terminals of the supply falls.
What is the other effect that internal resistance has on a source of E.M.F?
The source of the E.M.F is less than 100% efficient as energy is dissipated as heat within it.
What is the definition of open-circuit voltage?
Open-circuit voltage is the voltage measured across its terminals when no current is being drawn from it.
What is the definition of closed-circuit voltage?
Closed-circuit voltage is the voltage measured across its terminals when current is being drawn from it.
What is the internal resistance of a source of E.M.F thought of as?
It is thought of as resistance in series with the supply.
What do each of the symbols correlate to?
E = E.M.F of the cell, V = voltage across the terminals, r = internal resistance, R = load resistance, V = voltage lost in internal resistance.
How do you work out the total resistance of a circuit?
Total Resistance = R (Load Resistance) + r (Internal Resistance)
What are the two equations for the E.M.F of a circuit?
E = V + Ir
E = IR + Ir
What is one of the equations for the current in a circuit?
I = E / (R + r)
What is the potential difference across the load resistance known as?
It is known as the terminal potential difference, V, where V = IR.
What is the equation for E.M.F when both sides of it are multiplied by current, I?
EI = VI + I^2r
EI, is the power released by chemical energy in the battery. VI, is the power delivered to the external circuit. I^2r, is the power dissipated in the internal resistance of the battery.
In the experiment to find the internal resistance of a cell, what does the gradient of the line represent?
The gradient of the line is internal resistance, r.
How would you find the E.M.F using the graph?
You would extrapolate the graph backwards to cross the y-axis (Voltage). The voltage at which it crosses is the E.M.F of the cell.
