Megastar, let's knock this out.
Here are the answers for questions 1 through 5.
1a) State and explain the three main types of temperature scales.
The three main types of temperature scales are:
- Celsius Scale (∘C): This scale sets the freezing point of water at 0∘C and the boiling point at 100∘C at standard atmospheric pressure. It is widely used in most countries for everyday temperature measurements.
- Fahrenheit Scale (∘F): This scale sets the freezing point of water at 32∘F and the boiling point at 212∘F at standard atmospheric pressure. It is primarily used in the United States.
- Kelvin Scale (K): This is an absolute temperature scale, meaning 0K (absolute zero) is the lowest possible temperature where all molecular motion ceases. It is the standard unit of temperature in the International System of Units (SI) and is used extensively in scientific work.
1b) State the type(s) of thermometric substance used in:
- (i) Clinical Thermometer: Mercury or alcohol.
- (ii) Resistance thermometer: Platinum.
1c) List two similarities between Temperature and Heat.
- Both are related to the internal energy of a system.
- Both are forms of energy or measures of energy.
2a) Write down the temperature conversion equations when conversion is made from:
- (i) Degrees Celsius to degrees Kelvin:
K=C+273.15
- (ii) Degrees Kelvin to degrees Fahrenheit:
F=(K−273.15)×59+32
- (iii) Degrees Fahrenheit to degrees Kelvin:
K=(F−32)×95+273.15
- (iv) Degrees Fahrenheit to degrees Celsius:
C=(F−32)×95
2b) Two clinical thermometers recorded the normal human temperatures as 37 degrees celsius and 310 degrees Kelvin respectively. What is the sum of their reading in Fahrenheit?
Step 1: Convert 37∘C to Fahrenheit.
F1=(37×59)+32
F1=(66.6)+32
F1=98.6∘F
Step 2: Convert 310K to Fahrenheit. First convert to Celsius: C=K−273.15=310−273.15=36.85∘C.
Then convert Celsius to Fahrenheit:
F2=(36.85×59)+32
F2=(66.33)+32
F2=98.33∘F
Step 3: Sum the two Fahrenheit readings.
Sum=F1+F2=98.6∘F+98.33∘F
Sum=196.93∘F
The final answer is 196.93∘F.
3a) State 3 applications and 3 limitations of Newton's law of cooling.
Applications:
- Predicting the cooling time of hot objects, such as food or beverages.
- Designing cooling systems for electronic devices or engines.
- Estimating the time of death in forensic science.
Limitations:
- Assumes the surrounding temperature remains constant.
- Assumes the object's temperature is uniform throughout.
- It is most accurate for small temperature differences between the object and its surroundings.
3b) Water is heated to 80 degrees Celsius for 10 minutes. How much would be its temperature in degrees Kelvin if k=0.056 per minute and the surrounding temperature is 25 degrees Celsius.
Step 1: Convert initial and surrounding temperatures to Kelvin.
Initial temperature, T0=80∘C=80+273.15=353.15K.
Surrounding temperature, Ts=25∘C=25+273.15=298.15K.
Given time, t=10 minutes.
Given cooling constant, k=0.056min−1.
Step 2: Apply Newton's Law of Cooling formula: T(t)=Ts+(T0−Ts)e−kt.
T(10)=298.15+(353.15−298.15)e−(0.056)(10)
T(10)=298.15+(55)e−0.56
Step 3: Calculate e−0.56.
e−0.56≈0.5712
Step 4: Substitute and calculate T(10).
T(10)=298.15+(55)(0.5712)
T(10)=298.15+31.416
T(10)=329.566K
The final answer is 329.57K.
4a) Enumerate the following terms:
- (i) Number of moles (n): A unit of measurement for the amount of substance in the International System of Units (SI). One mole contains exactly 6.022×1023 elementary entities (atoms, molecules, ions, etc.).
- (ii) Number of molecules (N): The total count of individual molecules present in a given sample of a substance.
- (iii) Avogadro number (NA): The number of constituent particles (usually atoms or molecules) that are contained in one mole of a substance. Its value is approximately 6.022×1023mol−1.
4b) Identify the equation PV=NkT and show that it is equal to PV=nRT.
Step 1: Identify the equation.
PV=NkT is the ideal gas law in its microscopic form, where:
- P is pressure
- V is volume
- N is the number of molecules
- k is the Boltzmann constant (1.38×10−23 J/K)
- T is the absolute temperature
Step 2: Relate N to n using Avogadro's number (NA).
The number of molecules (N) is equal to the number of moles (n) multiplied by Avogadro's number (NA):
N=nNA
Step 3: Relate the Boltzmann constant (k) to the ideal gas constant (R).
The ideal gas constant (R) is the product of the Boltzmann constant (k) and Avogadro's number (NA):
R=NAk
Step 4: Substitute these relationships into PV=NkT.
Substitute N=nNA into the equation:
PV=(nNA)kT
Rearrange the terms:
PV=n(NAk)T
Now substitute R=NAk:
PV=nRT
This shows that PV=NkT is equivalent to PV=nRT, which is the macroscopic form of the ideal gas law.
4c) State the three salient features of Brownian movement.
- The motion is random and zigzag, with no definite direction.
- The motion is continuous and never stops, as long as the particles are suspended in the fluid.
- The motion is independent of the nature of the particles, but depends on factors like the size of the particles, the temperature of the medium, and the viscosity of the medium.
5a) Explain the mechanisms of heat transfer (b) write the formulars for the rate of heat loss by conduction and radiation.
Mechanisms of Heat Transfer:
- Conduction: Heat transfer through direct contact between particles. Energy is transferred from more energetic particles to less energetic ones through collisions, without any bulk movement of the material itself. It is common in solids.
- Convection: Heat transfer through the movement of fluids (liquids or gases). Warmer, less dense fluid rises, and cooler, denser fluid sinks, creating convection currents that transfer heat.
- Radiation: Heat transfer through electromagnetic waves. Unlike conduction and convection, radiation does not require a medium and can occur through a vacuum. All objects above absolute zero emit thermal radiation.
Formulas for the rate of heat loss:
-
Conduction (Fourier's Law):
tQ=kAL(T1−T2)
Where:
- tQ is the rate of heat transfer (power in Watts)
- k is the thermal conductivity of the material (W/(m⋅K))
- A is the cross-sectional area (m2)
- T1−T2 is the temperature difference across the material (K)
- L is the thickness of the material (m)
-
Radiation (Stefan-Boltzmann Law):
tQ=ϵσA(T4−Ts4)
Where: