Chapter 9 - Energy, power and resistance

Question 1

symbol for a cell

Answer 1

Just 1 cell

Question 2

symbol for a battery

Answer 2

More than 1 cells

Question 3

symbol for diode

Answer 3

A triangle and a line.

It only lets current flow in one direction.

Question 4

symbol for a variable resistor

Answer 4

a resistor with an arrow going up

You can adjust the amount of resistance if can offer.

Question 5

symbol for a fuse

Answer 5

a box with the wire going through

Question 6

symbol for a thermistor

Answer 6

a resistor with a hockey stick going through it

changes resistance based on temperature

Question 7

symbol for LDR

Answer 7

resistor with 2 arrows going into it (the left side)

ldr- light dependant resistance

Question 8

symbol for LED

Answer 8

A diode with 2 arrows going away from it (the right side)

led- light emitting diode

Question 9

symbol for capacitor

Answer 9

a battery expect that the 2 lines are the same

Question 10

what is 1 volt

Answer 10

the pd across a component when 1J of energy is transferred per unit of charge

Question 11

SI units for 1V

Answer 11

V = W / Q
V = J / C
V = kg⋅m2⋅s−2 / As

Question 12

Why do voltmeters have the highest resistance?

Answer 12

It’s so that no current can pass through them. If it did, it wouldn’t be able to measure the difference between them.

Question 13

EMF

Answer 13

Electromotive Force

The source of current such as a cell or a power supply.

Question 14

Difference between emf and pd

Answer 14

Potential difference is the energy dissipated as the unit charge passes through the components. The emf is the source of this current.

Question 15

Equation for emf

Answer 15

EMF = W / Q

Question 16

Energy transfer for electrons

Answer 16

eV= 1/2 mv^2

Question 17

What is an electron gun

Answer 17

It is used to produce a narrow beam of electrons, which can have precisely determined kinetic energies.

Question 18

Explain how an electron gun works

Answer 18

If the source is a filament that is heated up to release electrons, this process is called thermionic emission. The electrons on the filament gain kinetic energy, and some may actually leave the filament. Then they go through a very small slit (anode) to produce a thin beam of electrons. As they accelerate towards the anode, they gain kinetic energy.

Question 19

mass of an electron

Answer 19

1.1 * 10 -31

Question 20

What is resistance

Answer 20

It restricts the flow of charge carriers through it.

Question 21

equation for resistance

Answer 21

V = IR

Question 22

Ohm’s Law

Answer 22

For a metallic conductor kept at a constant temperature, the current in the wire is directly proportional to the pd across it.
(aka if pd is doubled, current also needs to be doubled)

Question 23

how does resistance change with temperature

Answer 23

the current in the circuit changes because the temperature of the wire increases over time as a result of heating caused by the current. As the wire gets hotter, the resistance increases.

Question 24

How do ions relate to resistance

Answer 24

Ions have more energy, therefore they vibrate with a greater amplitude, so the frequency of collisions increases and charge carriers do more work and transfer more energy.

Question 25

What is power

Answer 25

It is the rate of energy transfer by each electrical component is the power.

Question 26

Equation for power

Answer 26

P = I2 R
P = V2 / R
P = VQ / t