Module 4 Part 1- Electricity

Question 1

What is Kirchhoff’s first law

Answer 1

At any junction in a circuit,
the total current entering the junction is equal to
the total current exiting the junction

Question 2

What is Kirchhoff’s second law

Answer 2

In any circuit,
the sum of the emf is equal to
the sum of the pd
around a closed loop
Therefore energy is conserved

Question 3

How do you calculate the total resistance of a SERIES circuit

Answer 3

R1+R2+R3=RT

Question 4

How do u calculate the resistance in a PARALLEL circuit

Answer 4

1/R1 + 1/R2 + 1/R3 = 1/RT

Question 5

What is emf (electro motive force)

Answer 5

EMF is the energy transferred to the charge carries by the power source

Question 6

What is voltage/how does it differ from emf

Answer 6

Voltage is the energy transferred by the charge carries around the circuit not just the energy from the power source whereas emf is the energy transferred from the power source to the charge carriers.

Question 7

What is the equation that links current charge and time

Answer 7

I=change in Q/change in t

Question 8

What is the SI unit for charge and what is the assigned letter

Answer 8

coloumb which is given by the letter Q

Question 9

What is the elementary charge and what state the number

Answer 9

The elementary charge is the charge that one electron or proton holds and is presented by the letter e
The quantity is:1.6x10^-19

Question 10

What is the difference between conventional current and electron flow

Answer 10

Conventional current flows from the positive to the negative terminal
Electron flow flows from the negative terminal to the positive
Usually electron flow is what is used

Question 11

What is the equation for current

Answer 11

Current = change in charge/ change in time

Question 12

What is charge

Answer 12

Electric charge is a physical property of a particle that can either be positive or negative

Question 13

What are the two types of charge and how do they interact

Answer 13

Positive and negative
Like charges repel
Opposite charges attract

Question 14

What is the charge of an electron (and a proton)

Answer 14

1.6 x10^-19

Question 15

What is an electric current

Answer 15

Electric current is the moving of charge by a charge carrier

Question 16

What are some types of charge carrier

Answer 16

Some charge carriers are:
Electrons
Protons
Ions

Question 17

What is the difference between electron flow and conventional current

Answer 17

Electron flow is from negative to positive terminal
Conventional current is from positive to negative terminal

Question 18

What is number density and what does it mean

Answer 18

Number density of a material is the number of charge carriers available per cubic meter
The higher their number density the better an electric conductor it is

Question 19

What is mean drift velocity

Answer 19

Mean drift velocity is the average speed that the electrons in the wire move across the terminals

Question 20

What is the equation linking current, area, number density, charge and mean drift velocity

Answer 20

I=Anev

Question 21

What are the rules for a circuit diagram

Answer 21

Straight lines
No gaps

Question 22

What is the difference between a cell and a battery

Answer 22

A battery is multiple cells used together

Question 23

What is the electron gun

Answer 23

An electron gun is a device that produces a narrow beam of electrons by generating a p.d between a cathode and anode

Question 24

What is resistance and what is the equation that links voltage, current and resistance

Answer 24

Every component in a circuit has resistance and it is defined as the potential difference across a component over the current in the component.
This is given by when V=IR is re arranged into R=V/I

Question 25

What is a diode

Answer 25

A diode is an electrical component made from a semiconductor which only allows current through it in one direction

Question 26

What is an LED

Answer 26

A light emitting diode is a special type of diode which contains a semiconducting material which gives off light when a current passes through

Question 27

What it is resistivity

Answer 27

Resistivity is the constant given to a specific material which indicates how much resistance it puts up to current

Question 28

What three factors change the resistance

Answer 28

Resistivity, length and cross sectional area

Question 29

What is the difference between a conductor, semiconductor and insulator

Answer 29

Conductor-allows flow of electrons
Insulator-does not allow flow of electrons
Semiconductor-somewhere in between

Question 30

What is a thermistor

Answer 30

A thermistor is an electrical component made of a semiconductor with a negative temperature co-efficient therefore when temperature increases the resistance drops due to a higher number density in the semiconductor

Question 31

What is an LDR and how does it work

Answer 31

An LDR is an electrical component which drops in resistance as the light intensity increases
it works via a semiconductor in which the free electrons number density increases when the brightness increases

Question 32

What is internal resistance and how does it differ from batteries

Answer 32

Internal resistance is the resistance inside the battery that the emf has to overcome, a low internal resistance is used when a high current needs to be generated

Question 33

What is potential divider circuit

Answer 33

A potential divider circuit is a circuit that splits the potential difference over two resistors by using the principle that voltage is proportional to the resistance on each resistor which can be expressed as V1/V2=R1/R2

Question 34

What is a potentiometer

Answer 34

A potentiometer is a variable resistor with two terminals and one sliding terminal on top to allow a variable V out