Electricity E08-E13 Flashcards
What is EMF?
The electromagnetic force is the energy transferred or supplied per unit charge.
What is internal resistance?
Resistance within the actual power source (like a cell) itself, which means some emf is used (the lots volts).
What is the terminal p.d.?
The amount of actual volts that travel round the circuit and is used.
Imagine a V-I graph for the total emf in a cell. What does the gradient tell you?
The internal resistance
Imagine a V-I graph for the total emf in a cell. What does the y-intercept tell you?
The total EMF
Why does terminal p.d. across the cell depend on current?
As the current drawn from the cell increases the p.d. across the cell (terminal p.d.) decreases.
How do we calculate the total EMF and internal resistance of two cells in series?
The EMF and internal resistance are both added together when in series.
How do we calculate the total EMF and internal resistance of two cells in parallel?
The total EMF is whatever reading is off each branch.
The internal resistance is 1/R1 + 1/R2 = 1/RT (total).
How do we calculate the total resistance of resistors in series?
Add the resistors together.
How do we calculate the total resistance of resistors in parallel?
1/R1 + 1/R2 = 1/RT (total).
What is a potential divider?
A potential divider is used to supply constant or variable potential difference from a power supply.
What does a potential divider circuit look like?
The battery at the top.
Two resistors in series, one is fixed one is a variable resistor.
A voltmeter is placed around the variable resistor.
How can we make a sensor from a potential divider circuit?
A sensor can be made from the potential divider circuit by decreasing the variable resistor, let’s call it an LDR which decreases as light intensity increases. This results in an overall decrease in resistance in the circuit so current therefore increases with a fixed voltage. Therefore the voltmeter readings decreases.
What is the ideal resistance for a voltmeter?
Having zero to check the total resistance across the whole circuit, and infinite resistance to see how much voltage is following through it at it’s max, is ideal in a voltmeter.
What is the ideal resistance for an ammeter?
Having zero to check the total resistance across the whole circuit, and infinite resistance to see how much voltage is following through it at it’s max, is ideal in an ammeter.
