WEEK 3 NOTES

Question 1

What is the emf?

Answer 1

The emf is the potential difference of the source when there is no current flowing

Question 2

What are the two parts of a voltage source?

Answer 2

The emf and internal resistance

Question 3

What is terminal voltage?

Answer 3

It is the potential difference between positive and negative terminals of a battery

Question 4

At what point is the emf equal to the terminal voltage?

Answer 4

When no current is flowing through an open circuit

Question 5

At what point is the emf bigger than the terminal voltage?

Answer 5

When there is a current flowing through the circuit

Question 6

What is the maximum power transfer therom?

Answer 6

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

Question 7

What two devices can measure I, V and R?

Answer 7

Devices based on a traditional analogue moving coil galvanometer.
Devices based on a digital voltmeter/ multimeter

Question 8

Why are digital devices more common?

Answer 8

They are more precise, more robust and are easier to read

Question 9

When does a short circuit occur?

Answer 9

When an electrical current flows through an unintended path with zero/very little resistance.

Question 10

Why do short circuits happen?

Answer 10

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

Question 11

What do short circuits lead to?

Answer 11

Excessive current flow, which generates heat, damages components and sometimes causes fires

Question 12

What is a multimeter?

Answer 12

A digital device that measures multiple electric properties

Question 13

What are the 3 components to a multimeter?

Answer 13

Voltmeter- voltage measurement
Ohmmeter- resistance measurement
Ammeter- current measurement

Question 14

What does COM stand for?

Answer 14

Common, it is connected to the ground.

Question 15

What kind of circuit must an ammeter be connected in?

Answer 15

A series circuit

Question 16

What is the role of a fuse?

Answer 16

Fuses break the circuit in an appliance if too much current is flowing. This protects the appliance and wiring.

Question 17

Where should a voltmeter be situated to measure voltage?

Answer 17

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

Question 18

What does connecting a voltmeter to a circuit add?

Answer 18

It adds a resistance equal to the voltmeter resistance between the 2 points it is connected. This results in a change of PD

Question 19

What does connecting an ammeter add to a circuit?

Answer 19

It adds a resistance equal to the resistance of the ammeter. This changes the current that flows

Question 20

What are breadboards used for?

Answer 20

Rapid prototyping, they are not built to last. They operate with low voltages causing lower currents

Question 21

What does a wheatstone bridge do?

Answer 21

Its an alternative method of measuring resistance, when resistance is unknown

Question 22

What is a wheatstone bridge made of?

Answer 22

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)

Question 23

How do you find the resistance using a wheatstone bridge?

Answer 23

You adjust the variable resistor (Rs) until the voltmeter reads 0. At this point the bridge is said to be balanced. (Vout= 0V)

Question 24

When is a wheatstone bridge used?

Answer 24

With transducers to measure physical quantities e.g., temp

Question 25

What does it mean when the bridges are balanced in a wheatstone bridge?

Answer 25

The voltage across R1, R2 are the same and the voltage across R3, Rs are the same.

Question 26

What is Kirchhoff’s current law/ KCL?

Answer 26

States that the total current entering a circuits junction is equal to the total current leaving the same junction.

Question 27

What is Kirchhoff’s Voltage law/ KVL?

Answer 27

It states the sum of the voltage drops around a closed loop is equal to the emf

Question 28

What is a thermistor?

Answer 28

A type of resistor whose resistance is dependent on temperature.