Topic 2 Energy

Question 1

What is the SI unit of energy?

Answer 1

Joules (J) are the SI units of energy.

Question 2

What are the units of power?

Answer 2

Power is measured in watts (W). One watt is equivalent to one joule of energy being used per second.

Question 3

What is a kilowatt hour (kWh)?

Answer 3

This is the amount of energy that something with a power of 1 kW would use if it van continuously for 1 hour.

Question 4

What is electric current?

Answer 4

The flow of charged particles. Current (I) is the rate of flow of electric charge (Q), so

I = Q / t

The unit of current is an ampere (A).

Question 5

What is the conservation of energy?

Answer 5

Energy cannot be created on destroyed, so must always be accounted for.

Question 6

How are speed and mass proportional to kinetic energy?

Answer 6

Mass is directly proportional to kinetic energy.

Kinetic energy is directly proportional to speed squared.

Expressed by the equation. Ek = Cv^2

Where C is a constant value that relates kinetic energy to the speed squared.

Question 7

How to calculate the proportionality of forces?

Answer 7

You can divide one by the other i.e.

Ek at 100mph / Ek at 71mph = C x 100^2 / C x 71^2

=(100/71)^2
=1.4085^2
=1.98 =2

The ball traveling at 100 mph has twice the kinetic energy of the ball traveling at 71 mph,

Question 8

Kinetic energy equation

Answer 8

Ek (J) = 1/2 mv^2

Where m is in kg and v is m/s.

Question 9

Equation for gravitational potential energy

Answer 9

Eg (J) = mgh

Where m is mass (kg), g is acceleration due to gravity (9.81 m/s/s on earth) and h is vertical height (m) of the object.

Question 10

Equation for speed of falling (no air resistance)

Answer 10

V = gt

Where g is acceleration due to gravity (9.81 m/s/s) and t is time (s)

Question 11

Equation for speed of falling (no air resistance)

Answer 11

V = gt

Where g is acceleration due to gravity (9.81 m/s/s) and t is time (s)

Question 12

Calculate final speed

Answer 12

v^2 - u^2 = 2gΔh

Where v is final speed, u is initial speed, g is acceleration due to gravity and Δh is change in height.

Question 13

Calculate final speed

Answer 13

v^2 - u^2 = 2gΔh

Where v is final speed, u is initial speed, g is acceleration due to gravity and Δh is change in height.

Question 14

Planets gravitational potential energy equation.

Answer 14

Eg planet = - (G Ms(sun) m(planet)) / r

Where g is newtons gravitational constant (6.67x10^-11), M is the mass of the sun (1.99x10^30 kg), m is the mass of the planet and r is the radius

Question 15

What is electrostatic potential energy?

Answer 15

The potential energy that an object has because it is electrically charged.

The change in electrical energy (ΔEelec) when electric charges (Q) moves through a voltage difference (ΔV) is given by the equation

ΔEelec = QΔV

Question 16

What is potential difference?

Answer 16

This is related to the potential energy of a charged particle. it is the measurement of the difference between a reference point and the potential energy available.

Measured in volts.

Question 17

Electric Potential energy equation.

Answer 17

Eel = VQ

Where Eel is in J, V is volts and Q is is charge in coulombs (C)

Question 18

Measure potential difference and equation

Answer 18

To measure potential difference you place your reference probe anywhere and your test probe anywhere else. You can then subtract your reference point from your test point.

Potential difference = test probe potential - reference probe potential

Question 19

Converting mAh to coulombs

Answer 19

1 amp = 1 couloumb per second

So 860 mAh = 0.860 C/s x 3600 s =4644 J = 4.6 kJ

Question 20

What is ** work **? (Equation)

Answer 20

This is the amount of energy transferred when by applying force to an object.

Work (J) = force applied (N) x distance moved in the direction of force (m)

W = F x I

Question 21

What is pressure? (equation)

Answer 21

Pressure is defined as the force acting on an object per unit area.

Pressure (P) (Pa) = Force (F) (N) / area (A) (m^2)

Question 22

Equation for work done on gas.

Answer 22

Work = pressure x change in volume

W = PΔV

Question 23

Key point: the potential energy of matter.

Answer 23

The arrangement of particles in matter has a potential energy associated with it.

Question 24

What is heat?

Answer 24

Heat is the transfer of energy that occurs due to a temperature difference.

Question 25

What is absolute zero?

Answer 25

This is the coldest temperature possible zero kelvin or -273° C.

at this temperature all particle movement stops.

Question 26

What is the triple point of water?

Answer 26

This is a special state of water at a pressure of 611.2 Pa where solid, liquid and gaseous forms all coexist. The temperature of this state is defined as 237.16K

Question 27

How is energy transferred within each state?

Answer 27

• Gasses - via collisions.
• liquids - via collisions and via interparticle forces.
• solids - via the interparticle forces.