WEEK 3 NOTES Flashcards
What is the emf?
The emf is the potential difference of the source when there is no current flowing
What are the two parts of a voltage source?
The emf and internal resistance
What is terminal voltage?
It is the potential difference between positive and negative terminals of a battery
At what point is the emf equal to the terminal voltage?
When no current is flowing through an open circuit
At what point is the emf bigger than the terminal voltage?
When there is a current flowing through the circuit
What is the maximum power transfer therom?
It states that the DC voltage source will deliver maximum power to the variable load resistor when the load resistance is equal to the internal resistance
What two devices can measure I, V and R?
Devices based on a traditional analogue moving coil galvanometer.
Devices based on a digital voltmeter/ multimeter
Why are digital devices more common?
They are more precise, more robust and are easier to read
When does a short circuit occur?
When an electrical current flows through an unintended path with zero/very little resistance.
Why do short circuits happen?
Usually happens because 2 points of a circuit that should not be in contact come in contact with each other due to: faulty wiring, damaged insultation etc
What do short circuits lead to?
Excessive current flow, which generates heat, damages components and sometimes causes fires
What is a multimeter?
A digital device that measures multiple electric properties
What are the 3 components to a multimeter?
Voltmeter- voltage measurement
Ohmmeter- resistance measurement
Ammeter- current measurement
What does COM stand for?
Common, it is connected to the ground.
What kind of circuit must an ammeter be connected in?
A series circuit
What is the role of a fuse?
Fuses break the circuit in an appliance if too much current is flowing. This protects the appliance and wiring.
Where should a voltmeter be situated to measure voltage?
It must be in parallel with the part of the circuit that is being measured.
E.g. measuring the voltage drop across a resistor, the voltmeter would have to be parallel to that voltmeter
What does connecting a voltmeter to a circuit add?
It adds a resistance equal to the voltmeter resistance between the 2 points it is connected. This results in a change of PD
What does connecting an ammeter add to a circuit?
It adds a resistance equal to the resistance of the ammeter. This changes the current that flows
What are breadboards used for?
Rapid prototyping, they are not built to last. They operate with low voltages causing lower currents
What does a wheatstone bridge do?
Its an alternative method of measuring resistance, when resistance is unknown
What is a wheatstone bridge made of?
Two potential dividers:
One consisting of two known resistors. (R1, R2)
The other consisting of the unknown resistor in series with a calibrated variable resistor. (R?, Rs)
How do you find the resistance using a wheatstone bridge?
You adjust the variable resistor (Rs) until the voltmeter reads 0. At this point the bridge is said to be balanced. (Vout= 0V)
When is a wheatstone bridge used?
With transducers to measure physical quantities e.g., temp
What does it mean when the bridges are balanced in a wheatstone bridge?
The voltage across R1, R2 are the same and the voltage across R3, Rs are the same.
What is Kirchhoff’s current law/ KCL?
States that the total current entering a circuits junction is equal to the total current leaving the same junction.
What is Kirchhoff’s Voltage law/ KVL?
It states the sum of the voltage drops around a closed loop is equal to the emf
What is a thermistor?
A type of resistor whose resistance is dependent on temperature.
