Chapter 9 - Energy, Power And Resistance

Question 1

What is the function of the cell ?

Answer 1

Pushes charge around the circuit

Question 2

What is the function of a Ammeter ?

Answer 2

Measure the current in the circuit

Question 3

What does the Voltmeter do ?

Answer 3

It measures the Voltage or pd in a circuit

Question 4

What does a filament lamp do ?

Answer 4

A filament lamp emits light when current passes through it

Question 5

What is an LDR and what does it do ?

Answer 5

An LDR is a Light dependent resistor

In bright light the resistance falls
In darkness the resistance is highest

Question 6

What does a fuse do ?

Answer 6

A fuse contains a piece of wire that melts easily so if there is a very high current going through the fuse the write heats up until it breaks the circuit.

Basically the fuse breaks the circuit in order to protect the wiring

You can get fuses that melt at different currents

Question 7

What does a resistor do ?

Answer 7

A resistor limits the electric current in a circuit

Question 8

What does an LED do ?

Answer 8

A Light emitting diode, emits light when a electrical current passes through it

Question 9

What does a switch do ?

Answer 9

A switch can be used to cut off the current being pushed around a circuit. It can be used to break the circuit and can be used to complete a circuit

Question 10

What is a thermistor ? And what does it do ?

Answer 10

A thermistor is a temperature dependent resistor.

In hot conditions, the resistance falls
In cool conditions, the resistance goes up

Question 11

What is a variable resistor ?

Answer 11

A variable resistor is one that can have its resistance varied and therefore can also vary the potential difference/current

Question 12

What is voltage a measure of ?

Answer 12

Voltage is a measure of the electrical energy transferred per unit charge.

It can be defined as the amount of work done per unit charge

Question 13

What is voltage a difference of ?

Answer 13

Voltage is measured as a difference in energy between 2 points. Thus a voltmeter must be connected in parallel and is used to measure the difference in pd across a device

Question 14

Whats the equation for voltage ?

Answer 14

V = W / Q

Question 15

What is one Volt defined as ?

Answer 15

One volt is defined as the energy transferred Per coulomb of charge as the charges move between 2 points in a circuit

Question 16

Whats the resistance of the voltmeter and why ?

Answer 16

You don’t want any current flowing through the voltmeter so company’s make them have a very high resistance ( infinite resistance )

Question 17

What does 1V =

Answer 17

1V = 1JC -1

Question 18

What’s the electromotive force ?

Answer 18

EMF is the energy transferred to the charge carriers by the cell/battery

Question 19

What is potential difference ?

Answer 19

Pd is the energy transferred by the charge carriers ( the work done by the charge carriers )

Question 20

Whats the term used to describe when work is done ?

Answer 20

The term used to describe when work is done is energy transferred

Question 21

What is resistance of a component ?

Answer 21

The resistance of a component is defined as the ratio between the potential difference across the component and the current flowing through it

Question 22

What is the equation for resistance ?

Answer 22

R = V / I

Or V = IR

Question 23

Whats resistance measured in ?

Answer 23

Ohms ( Omega symbol )

Question 24

What is one Ohm equal to ?

Answer 24

1 ohm = 1 VA -1

Question 25

What is Ohms law ?

Answer 25

For a metallic conductor at a constant temperature, the pd across the conductor is directly proportional to the current flowing through it

Ohms law essentially = V = IR

Question 26

How do you calculate the resistance from an IV graph ?

Answer 26

The gradient is the resistance

Question 27

Why does resistance increase with temp ?

Answer 27

Because when the metal gets hotter, the metal ions inside the lattice start to vibrate move and therefore make it harder for the charge carriers to flow through them.

Question 28

What is Kirchhoff’s second law ?

Answer 28

In any circuit, the sum of the electromotive forces is equal to the sum of the pd around a closed loop

Question 29

What physical quantity conserved in Kirchhoff’s first law ? And second law

Answer 29

Charge is conserved in the first law
Energy is conserved in the second law

Question 30

What is terminal pd ?

Answer 30

It’s the amount of energy available to the rest of the circuit after some of the energy has been lost in the cell as heat due to the internal resistor inside the cell

Question 31

What is the lost energy called that happens due to the internal resistance of the cell ?

Answer 31

Lost Volts

Question 32

How is the terminal pd found out ?

Answer 32

It’s the e.m.f supplied to the cell, minus the energy lost (lost volts) in the cell as heat

Question 33

What does electromotive force =

Answer 33

Terminal pd + lost volts

Question 34

What is resistance ?

Answer 34

Resistance is a measure of the opposition to current flow in an electrical circuit

Question 35

What does resistance depend on ?

Answer 35

• cross sectional area
• material
• length
• temperature

Question 36

How is resistance affected by length ?

Answer 36

Resistance is directly proportional to length

Question 37

How is resistance affected by cross sectional area ?

Answer 37

Resistance is directly proportional to cross sectional area

Question 38

What is resistivity ?

Answer 38

The measure of how much a particular material opposes electron flow is called the resistivity of the material.

Question 39

What is resistivity usually given in ?

Answer 39

resistivity is usually given the symbol p - Greek letter rho

Question 40

Whats the equation for resistivity ? How do you re arrange for rho ?

Answer 40

Resistivity = resistance x cross-sectional area / length

Resistance = p
Cross sectional area = A
Resistance = R

Weird p = R x A / L