Chapter 5 - Direct current circuits Flashcards
In series what is true about the current?
The current is the same everywhere
At a junction in a circuit what is true?
The current leaving = the current entering
In a series circuit what is true about voltage?
The sum of the potential differences going through the components = the potential difference of the cell
In series what is true about resistance?
The sum of resistance = total resistance
In parallel what is true about current?
The total current through the branches = the current through the cell
In parallel what is true about voltage?
It is the same everywhere
In parallel what is true about resistance?
1/The sum of the reciprocals of the branches = resistance through the cell
Define the term internal resistance
Resistance inside the source of electrical energy when the current passes through it (loss of p.d. per unit current)
What is the formula relating current, power and resistance/voltage?
P=IIR=IV
What is the formula relating electromotive force, energy and charge?
Emf = E/Q
What is the formula relating power, energy and time?
P=E/t
What is the formula relating emf, current, resistor resistance (R), and internal resistance?
emf = I(R+r)
What is the formula relating emf, voltage, internal resistance and current?
emf=V+Ir
When is the maximum power delivered to the load?
When the loads resistance = internal resistance
How can you plot v=emf-Ir on a graph?
y=mx+c
V=-Ir+emf
On a graph how do you work out internal resistance?
Work out the gradient: change in voltage/ change in current
What are the 4 top tips to circuit questions?
Draw digram with ruler, calculate cell current, work out current and resistance for each resistor, work out p.d. in parallel resistors - cell current*combined resistance, then *by a ratio or resistor in that branch
If 2 cells are connected oppositely in series what should you do?
Subtract and resolve
When n identical cells are in parallel what is the current through each cell?
I(r)/n
How do you work out terminal potential difference for cells in parallel?
emf - Ir/n
How much voltage do diodes have in the forward direction?
0.6V and infinite <0.6V
Define the term potential divider
When 2 or more resistors in series are connected to a source of p.d.
In a potential divider what formula links 2 different resistances and 2 different voltages?
V1/V2=R1/R2
What can variable resistors be used for?
Controlling volume of a speaker or brightness of a bulb
Define the term sensor circuit
Where the output p.d. changes a result of a physical variable (light/temperature)
