Chapter 13 Flashcards
What is the current entering a junction/ component equal to?
The current leaving it
In series how does the current through different components compare?
It is the same.
For components in series, the total potential difference is?
Equal to the sum of potential differences across each component.
For components in parallel, how does each components potential difference compare?
They are equal
For any complete loop what does the sum of Emf’s round the loop equal?
It equals to sum of potential drops across the loop (when going through a component) - this conserves energy
For resistors in series, what does the total resistance equal?
The sum of individual resistances of the components
For resistors in parallel, what is the total resistance?
It is smaller that the resistance of the smallest resistor
What equation tells us how much energy is transferred due to resistive heating?
P = I^2 x R
Definition of Internal Resistance?
The loss of potential difference per unit of current in the source when current passes through the source
What is the equation to find the power supplied by the cell
P = IE
When is the max power delivered to the load ( think graph)
When the load resistance is equal to the internal resistance of the source.
How does putting cells in parallel affect the internal resistance?
It reduces the effects of the internal resistance
State the two Kirchoff’s laws
1) At any junction, total current entering is equal to the total current leaving
2) For any complete loop, sum of Emf’s around the loop equals the sum of potential drops around the loop
What three things can the potential divider be used for?
- To supply a potential difference (fixed at any value between 0 & the source pd)
- To supply a variable p.d
- To supply a p.d that varies with environmental conditions (e.g using a thermistor or LDR)
What is the circuit setup to supply a p.d that’s fixed at any value between zero and source p.d (current not zero)?
A cell (V’0) connected to R1 (V’1) and R2 (V’2) in series.
This means that I = V’0 / (R1 + R2)
Ratios of p.ds: V1/ V2= R’1/ R’2
How would you set up a circuit to supply a variable p.d?
Set up a cell (V’0) with a resistor and a device connected in parallel to it with a moving contact.
A moving contact allows a variable p.d across output device and allows current through the device to be 0
How would you set up a circuit to supply a p.d that varies with environmental conditions?
Set up a cell with a (either LDR or thermistor) and a variable resistor in series. (Have a voltmeter over the LDR/ thermistor). The variable resistor allows you to choose the p.d across the LDR/ thermistor for a particular lighting condition.
