Test 2 Energy & Thermal

Question 1

Absolute zero?

Answer 1

0K or -273°C. A purely theoretical value. Since all particles possess kinetic energy there will always be some temperature. Theoretically the electron would be stationary @absolute zero. At that point, everything would, theoretically, fall apart. Space has a temp of about 3K b/c of Bigbang background radiation.

Question 2

What does temperature indicate?

Answer 2

Temperature indicates in which direction heat will flow when two bodies are placed close together.

Question 3

Thermal energy?

Answer 3

Thermal energy is the component of a body’s internal energy due to its temperature. Can be supplied via heating. Heat is the thermal energy transferred from high temp to low temp to resolve Δtemp. Measured in joules! (w/s)

Question 4

Thermal equilibrium?

Answer 4

Hot -> Cold Once the bodies are @ the same temp there is no net flow of thermal energy. The bodies are in thermal equilibrium.

Question 5

T(K)=?

Ө(°C)=?

Answer 5

T(K) = Ө(°C)+273.15

Ө(°C) = -273.15

Question 6

Specific heat capacity?

Answer 6

The thermal energy required to raise the temperature of a body of mass 1kg by 1K.

Q = mcΔӨ

Q or E = thermal energy supplied to, or lost by, the body (J)

m = mass of body (kg)

c = specific heat capacity (Jkg^-1 K^-1)

ΔӨ = temperature change of body (K)

Question 7

Calculate the mass of ice-cold water that a person would need to drink in order to lose 0.5kg fat. 0.5kg of fat stores 1.6*10^8 J energy. SHC, c = 4200Jkg^-1K^-1 ΔӨ = 37°

Answer 7

m = Q/cΔӨ = (1.6*10^8) / (4200*37) = 1030 Answer: 1030kg

Question 8

Moon phases?

Answer 8

Question 9

Elementary charge?

Answer 9

e = 1.6*10^-19 C

Question 10

Boyle’s law?

Answer 10

Linking pressure and volume of gas.

P1V1 = P2V2

Question 11

Charles’ law?

Answer 11

Linking volume and temperature of gas.

V1/T1 = V2/T2

Question 12

Combined gas law?

Answer 12

P1V1/T1 = P2V2/T2

Question 13

Pressure?

Standard atmospheric pressure?

Answer 13

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

101kPA

Question 14

Specific latent heat?

Answer 14

the amount of energy needed to change the state of unit mass of a pure substance without a change in temperature.

Q = ml

Q = thermal energy supplied to, or lost by, the body (J)

m = mass (kg)

l = specific latent heat (Jkg^-1)

Question 15

How much energy is required to melt 5.00kg of ice given that its specific latent heat of fusion is 3.36*10^5 Jkg^-1?

Answer 15

Q = ml = 500*3.36*10^5 = 168000 = 1.68 MJ

Question 16

Kinetic theory of gases?

Answer 16

Macroscopic: gas takes volume of container. exerts pressure on the walls of the container.

Microscopic: gas in collection of particles that collide.

So the kinetic theory relates the pressure exerted by a gas to the motion of its particles.

pV = 1/3Nmc_(rms)

Question 17

Current?

Answer 17

A measure of the amount of charge moving per sec.

I (A) = ΔQ (C) / Δt (s)

When a potential difference (voltage) is applied across a conductor a current is produced.

Question 18

Electron flow?

Answer 18

Electrons flow from a circuit’s negative terminal to positve. Traditionally current is drawn flowing in opposite direction ( + -> - ), conventional current.

Question 19

Voltage?

Answer 19

Aka potential difference.

measure of energy provided to the charge carriers. Amount of work done per unit charge.

V(v) = W(J) / Q (c)

Question 20

If a cell supplies 23 coulombs of charge with 776J of energy what is its voltage?

Answer 20

V = 776/23 = 33.74

Question 21

Resistance?

Answer 21

measure of the opposition a material exerts against the flow of electrons.

R ( Ω ) = V(v) / I (A)

Question 22

Kirchoff’s 1st law?

Answer 22

The sum of the cuurrents leaving any junction is always equal to the sum of the currents that enter it.

Conservation of charge: no charge lost or made in circuit.

I = I1 + I2 + I3

Question 23

Kirchoff’s 2nd law?

Answer 23

The total voltage across a circuit loop is equal to the sum of the voltage drops across the devices in that loop.

Amount of e- stays the same though their energy have been converted (into eg light).

Vin = V1 + V2

Question 24

Ohm’s law?

Answer 24

The current in an ohmic conductor is proportional to the voltage across it, provided that the temperature and other physical conditions are kept constant.

V ∝ I

Question 25

Resistors in series?

Answer 25

Add resistor values together: RT = R1 + R2 + R3 From pic: RT = 10+20+15 = 45Ω

Question 26

Resistors in parallel?

Answer 26

1/RT = 1/R1 + 1/R2 + 1/R3 From pic: 1/RT = 1/10+1/20+1/15 =6+3+4/60 =13/60

Question 27

Resistivity?

Answer 27

The property of resistance. How much a particular material opposes electron flow. Resistivity (ρ) = (resistance \* cross-sectional area) / length ρ = RA / L

Question 28

Potential dividers?

Answer 28

Potential dividers reduce voltage. Varying the ratio of a pair of resistors changes the output voltage of a circuit. Vout = Vin \* (R2 / R1 + R2)

Question 29

Vin = 6 R1 = 10Ω R2 = 20Ω Vout?

Answer 29

Vout = Vin \* (R2 / (R1 + R2)) = 20 \* (6/(10+20)) =20\*0.2 =4V

Question 30

Power and energy in circuits?

Answer 30

The power (rate of energy transfer) of a device is a product of the voltage and the current passing thorugh the component. Power (W) = Voltage (V) \* Current (A) ALSO P = I^2R P = V^2/R P = IV

Question 31

Electrical energy?

Answer 31

Energy = current \* time \* voltage

Question 32

Electromotive force?

Answer 32

``` E = emf V = potential difference (p.d.) r = internal resistance of battery R = external resistance in circuit, I = current in the circuit ``` ``` **V = IR E = I(R+r) E = V + Ir** ```