electricity and molecules/matter

Question 1

Explain E =p x t

Answer 1

power (Watts) = energy transferred (joules)/ time (seconds)

Question 2

Define current, potential difference and power in terms of an appliance

Answer 2

• Current through it is the charge that flows through it each second
• The potential difference across it is the energy transferred to the appliance by each coulomb of charge that passes through it
  -The power supplied to it is the energy transferred to it each second. This is the energy transferred by an electric current every second.

Question 3

State the equation based on energy transfer to the appliance each second = the charge flow per second x the energy transfer per unit charge

Answer 3

power (watts) = current (Amp) x Potential Difference (Volts)

Question 4

Whats the equation of power supplied to a resistor

Answer 4

power (watts) = current squared x Resistance (ohms)

Question 5

What principle does the equation of power supplied to a resistor show?

Answer 5

The power supplied to a resistor is proportional to the square of the current. So if current is doubled, the power becomes four times more.

Question 6

How do you calculate the rating of a fuse?

Answer 6

electrical power (watts) / Potential difference ( volts)

Question 7

What’s the equation for the charge flow of an appliance?

Answer 7

charge flow (in coulombs) = current (amps) x time (secs)

Question 8

Why does a resistor become hot when charge flows through it?

Answer 8

Because energy is transferred to the resistor.

Question 9

How do you work out the energy transferred to a component?

Answer 9

E = V x Q energy = charge flow x potential difference

Question 10

How do you work out energy transferred from the mains?

Answer 10

E (joules) = power (watts) x time (seconds)

Question 11

How do you work out the power supplied to an electrical appliance?

Answer 11

power (watts) = current (amps) x potential difference (volts)

Question 12

How do you calculate energy efficiency?

Answer 12

efficiency = output power / input power ( x 100%)

Question 13

How do you work out output power, knowing the efficiency of an appliance?

Answer 13

output power = efficiency x its input power

Question 14

What is the definition of density

Answer 14

Density = mass kg / volume (metered cubed) = SUBSTANCE DEFINED AS MASS PER UNIT VOLUME

Question 15

What density or less do objects float at on water?

Answer 15

Less than the density of water = < 1000kg/m3

Question 16

What is the most dense state?

Answer 16

Solid

Question 17

Which state can have a large and variable volume?

Answer 17

Gas

Question 18

What does the conservation of mass mean?

Answer 18

The mass of a substance stays the same as the number of particles do not change, no matter the state it is in.

Question 19

Which states have fixed volumes?

Answer 19

Solid and liquid

Question 20

Which states can flow?

Answer 20

liquid and gas

Question 21

Describe the kinetic theory of matter

Answer 21

Solid particles are held next to each other in fixed positions/can vibrate. They are the least energetic/have the least energy. Liquid particles move but are still close together/in contact. They have more energy than solids. Gas particles move far apart and very quickly as they have the most energy.

Question 22

Define melting point

Answer 22

The temperature at which a solid turns into a liquid.

Question 23

Define boiling point

Answer 23

The temperature at which a liquid turns to a gas.

Question 24

Define freezing point

Answer 24

The temperature at which a liquid changes to a solid.

Question 25

what can measure the point of melting and freezing?

Answer 25

The melting point ( of a solid, then of a liquid)

Question 26

What can measure the point of boiling and condensing?

Answer 26

Boiling point (of a liquid, then of a gas)

Question 27

What is latent heat?

Answer 27

The energy transferred to a substance to change its state.

Question 28

When does evaporation occur?

Answer 28

it occurs at the surface of a liquid when its temperature is below its boiling point.

Question 29

What does the flat section of a temperature time graph show?

Answer 29

The melting point or the boiling point of a substance.

Question 30

What is internal energy?

Answer 30

The energy stored by the particles of a substance. It is caused by their motion. Particles gain energy as heat is applied to melt and boil. Particles lose energy when they solidify or freeze.

Question 31

what two things make up internal energy?

Answer 31

The kinetic energy they have due to their individual motions relative to one another and their potential energy due to individual positions relative to each other.

Question 32

What happens to the particle's kinetic energy stores when the substance is heated?

Answer 32

When temperature increases, the total kinetic energy of the particles increases also.

Question 33

What does the specific heat equation show?

Answer 33

The energy needed to change temperature without changing state.

Question 34

What happens to a particle's potential energy when it's physical state changes?

Answer 34

From solid to liquid (melting): Potential energy increases as particles move apart. From liquid to gas (evaporation): Potential energy increases further as particles move even further apart. From gas to liquid (condensation): Potential energy decreases as particles move closer together. From liquid to solid (freezing): Potential energy decreases as particles move closer together.

Question 35

What determines a substance's physical form to exist as a solid, liquid or gas?

Answer 35

The relative strength of forces of attraction between the particles of a substance. As solids are heated and melt to liquid then to gas, energy is gained, particles move away from each other and are less attracted to each other. (During this process determined by boiling point, internal energy increases, kinetic energy increases. If it was gas to solid, everything would be the other way around and determined by melting point, losing kinetic energy, internal energy of the states would get progressively lower ad there would be a greater strength of attraction between particles in the resulting solid rather than the original gas).

Question 36

What causes the pressure of a gas on a surface?

Answer 36

The particles repeatedly hitting the surface as they bounce around quickly to fill the space they are contained in.

Question 37

What is latent heat?

Answer 37

The energy needed for a substance to change its state without changing its temperature.

Question 38

What is the specific latent heat of fusion?

Answer 38

The energy needed to melt 1kg of a substance without chaning its temperature. The equation is E = m L L (specific latent heat) = Energy E in Joules / Mass M in kg