FQ - 2B - 17 de marzo de 2022

• Natuurkunde / Scheikunde
• Middelbare school
• havo
• Leerjaar 2

FQ - 2B

- repeat last class

- thermal expansion

- thermal equilibrium

- make exercises

Repetition

What is:

• kinetic energy
• thermal energy
• absolute zero
• heat
• What happens when adding heat?
• What is the relation between Kelvin and Celsius?

Which one has more kinetic energy?

What is the temperature?

80 °C

20 °C

Thermal extension

Listen carefully to the video.

Expansion in solids and liquids

linear expansion:

L = L₀ (1 + α x ΔT)

L = length of the bar

L_{0 = initial length before heating}

_{α = coefficient of linear expansion}

_{ΔT = variation in temperature}

Expansion in gases

Charles' Law

V = k x T

k = proportionality constant

Remember that the temperature is given in Kelvin when you make calculations using Charles' Law

Thermal equilibrium

= When two fysical bodies or systems at different temperatures come into contact, they end up having the same temperature

Heat is the transfer of energy from one body or

system with higher temperature to antoher with

a lower temperature.

Measurement of heat

Heat is measured in units of energy → joule (J).

Traditional unit is the calorie (cal). A calorie is defined as the amount of heat needed to heat a gram of water by one degree.

1 cal = 4,184 J

Let's practise

Make exercises 5 through 11.

Finished? Process the theory.

Answers

5. Alcohol, because the linear expansion coefficient is highest.

6. L = 1000 (1 + 1,1 * 10^-5 x 40) = 1000,44 m, so it has expanded
     0,44 m or 44 cm.

7. If they didn't use expansion joints, there could be potential distortion or breaks.

8. The flame is to heat the helium gas. This way the gas expands and the balloon goes up in the air.

Answers

9. 

                                                       V1 = (1 x 300) / 20 = 15 m³

10. a) 20 cal = 83,68 J                                  d) 4200 kJ = 1004 kcal

     b) 3000 J = 717 cal                                   e) 5000 cal = 1,195 kJ

     c) 1500 kcal = 6276 kJ                            f) 16400 J = 3,919 kcal

1 m 3	V 1
20 °C	300 °C