Electricity

Question 1

Definition of charge

Answer 1

Flow of electrons I x t = Q

Question 2

Shuttle ball experiment explaination

Answer 2

Plates initially have opposite charge.
Ball has conduction surface
When it touches the negative plane it picks up a few electrons and are repelled from the negative plate and attracted to the positive plate
It passes the electrons onto the positive plate and loses a bit more electrons and then bounces back
There is a current in the gap
As you increase pd the ball will accelerate more so there is a greater force due to f=m x a

Question 3

Definition of electric current

Answer 3

rate of flow of electric charge (Q) per unit time (t)

Question 4

Charge of an electron

Answer 4

1.6 x 10^-19

Question 5

Kirchhoff 1st law

Answer 5

the total electric current flowing into any junction (or node) in an electrical circuit must equal the total current flowing out of that junction, based on the conservation of charge.

Question 6

Drift velocity equation

Answer 6

(I=neAv_{d})

𝑣𝑑: Drift velocity (m/s) - the average velocity of charge carriers , Electric current (Amperes) , Number density of charge carriers (carriers per cubic meter) , Elementary charge (Coulombs, C) - the charge of a single electron (approx. (1.602\times 10^{-19}) C, (A)Cross-sectional area of the conductor (square meters, (m^{2})).

Question 7

What is electron gas and what do electrons do with and without current

Answer 7

When no current is flowing, the free electrons can be
thought of as an electron gas, randomly moving in all
directions. On average, the electrons do not move.
• However, when a current is flowing, there is a gradual
drift of the electrons in a particular direction.

Question 8

Difference between metal conductor and insulator

Answer 8

Metal conductor has a a high electron carrier density and therefore has a current. Insulators have negligible electron carrier density and therefore has no current

Question 9

Potential difference

Answer 9

A measure of the transfer of energy from charge carrier to component per unit charge

Question 10

Electromotive force

Answer 10

Work done on charge carriers per unit charge. From fuel cell chemical energy to electrical energy charge carriers

Question 11

Kirchhoff second law

Answer 11

Total EMF in a closed circuit loop is equal to the total pd in the closed circuit loop

Question 12

Resistance in series vs parallel

Answer 12

S: Rt = R1 + R2 …
P: 1/Rt = 1/R1 + 1/R2 …

Question 13

Ohms law

Answer 13

Given there is constant resistance and a constant temperature pd across a component is directly proportional to the current flowing through it

Question 14

Rules of circuit in series

Answer 14

Voltage split and current is constant

Question 15

Rules of parallel

Answer 15

Voltage is constant and current is split

Question 16

Volt

Answer 16

The pd across a component when 1 joule of energy is transferred per unit charge passing through a component

Question 17

IV characteristics of a resistor

Answer 17

Is an oh if conductor therefore v is dp to I so straight line graph

Question 18

IV characteristics of a filament lamp

Answer 18

Non-ohmic componente so resistance is not constant. V is not dp to I. Higher current causes increased temperature and therefore an increase in resistance because electrons transfer energy to the positive ions which vibrate and cause more collisions with charge carriers, blocking their path. So curved graph towards the x-axis at end points.

Question 19

IV characteristics of a diode or LED

Answer 19

Does not obey ohms law so non-ohmic component. The resistance is very high(infinite) in the negative polarity causing there to be zero current. In positive side as pd increases resistance begins to drop.

Question 20

IV characteristics of a thermistor

Answer 20

Semiconducting component so non-ohmic. As current increases the temperature increases. This temperature leads to a decrease in resistance because the number density of charge carriers increase. Graph curves at the end but away from x-axis

Question 21

What is meant by a non-ohmic component

Answer 21

Does not have constant resistance

Question 22

Explain in terms of resistance and bias how a diode is used in a circuit to control the direction of current flow

Answer 22

A diode only allows current to flow in one direction
This is the forward bias
Current only flows once the threshold pd has been exceeded usually 0.6V
In reverse bias , the resistance is very high so no current flows

Question 23

What happens to ammeter and voltmeter reading if a thermistor is heated

Answer 23

Resistance decreases so current increases because number density increases. Voltmeter reading does not change because there is no internal resistance.

Question 24

why is current lower when a battery pack is used rather than mains how does this effect resistance

Answer 24

because of lower voltage, higher internal resistance, and the need for efficiency in portable devices. Resistance is less as temperature does not increase as much

Question 25

State and explain how the velocity of an electron and a proton would compare when accelerated through the same pd

Answer 25

Electron would be faster than a proton. This is because kinetic energy would be equal as the magnitude of charge are equal. But mass of proton is larger so electron would travel faster at the same kinetic energy.

Question 26

Describe the difference between three materials ( copper carbon and ceramic) in terms of number density of free electron. Include an explanation of the term nd

Answer 26

Number density is the number of free charge carriers per unit volume. The larger n is the better the conduction. Cooler has the greatest n followed by carbon followed by ceramic

Question 27

Use of electron gun

Answer 27

Electron microscopes and particle acceleration and electron diffraction experiments

Question 28

Thermionic emission

Answer 28

The cathode is heated by passing a current through it, causing electrons to escape from its surface

Question 29

Definition of an electron volt and state its value in joules

Answer 29

Energy acquired by an electron accelerated through a pd of 1V 1eV = 1.6x10^-19 J

Question 30

Mean drift velocity meaning

Answer 30

The average displacement of electrons per unit time along the wire. On average the move slowly in one direction because they collide constantly

Question 31

Potentiometer

Answer 31

A variable resistor with three terminals and a sliding contact. Adjusting the contact varies pd between tow of the terminals giving a variable Vout.

Question 32

Internal resistance

Answer 32

The opposition to current flow within a power source due to its internal components causing energy dissipation as heat. This causes a voltage drop known as ‘“lost volts”

Question 33

What does lost volts entail about terminal pd and emf

Answer 33

That emf is always greater than terminal pd.

Question 34

Examples of internal resistance

Answer 34

Chemical cell = work done due to reaction between chemicals Solar cell = due to resistance of material of cell

Question 35

How to investigate internal resistance

Answer 35

Use a circuit with a battery and resistor connected with a voltmeter and then an ammeter in series and a variable resistor. Record different values for terminal pd for different values of current. Use variable resistor to change resistance of circuit, drawing different currents from power sources. Graphing : y = mx + c E =V + Ir —> V = -rI + E So plotting V against I will give a greasiest of -r and a y-intercept of E. According to the graph, as current increases, terminal pd drops and lost volts increases.

Question 36

KWH definition

Answer 36

The energy transferred by a component operating at 1KW for 1hour.

Question 37

If the temp of a thermistor decreases what happens to resistance, current and pd

Answer 37

Resistance increases, current is constant and pd increases

Question 38

Define pd

Answer 38

Word done per unit charge from electrical energy to any other form