Topic questions Particle model of matter Specific latent heat
11 questions · 91 marks · about 2 hours
Show that the mass of the ice sculpture is about 2.2
105kg.
density of ice = 920 kg m–3
Give two reasons why your analysis of the situation may be incorrect.
Chocolate is a solid at room temperature, but melts just below body temperature.
A student investigated the viscosity of some melted chocolate using a falling-ball method. Since chocolate is opaque, a thin rod was attached to the ball so that the movement of the ball could be monitored. The apparatus is shown in the diagram.
The chocolate was maintained at a constant temperature during the investigation.
The student used a stopwatch to measure the time t for the ball to fall 22.5 cm whilst travelling at its terminal velocity v.
Her results are shown in the table.
| t1 / s | t2 / s | t3 / s |
| 9.6 | 9.9 | 9.6 |
v is given by the formula
where r is the radius of the ball
The graph is taken from a commercial website. It shows how, at the temperature of the experiment, η depends on the percentage of cocoa in the chocolate.
The chocolate wrapper indicated that the chocolate had a 35% cocoa content.
Assess whether the student’s timing data supports this percentage cocoa content.
r = 4.25×10–3m
Explain one reason why the student’s data may have led to an inaccurate conclusion about the cocoa content.
One type of chocolate melts at a temperature of 32
C.
The energy released when 65 g of this chocolate is digested is 345 kcal.
It is suggested that the energy used to melt a piece of this chocolate is at least 15% of the energy released when the chocolate is digested.
Assess the accuracy of this suggestion.
initial temperature of chocolate = 15
C specific heat capacity of chocolate = 3.9103 J kg–1K–1 specific latent heat of chocolate = 1.50
105J kg–1 1 kcal = 4200 J
A student planned to vary the current in the heater from 0 A to 5 A. The student connected the following circuit to measure the current in the heater.
Criticise the student’s circuit.
The student corrected the circuit and closed the switch. He waited until the water started boiling. He started a stopwatch and recorded the readings on the balance at regular time intervals.
Sketch a graph, on the axes below, of how the readings on the balance would vary with time.
The heater was switched on for 6.0 minutes and the change in mass of water in the beaker was 7.5 g.
Calculate the specific latent heat of vaporisation of water, L.
V = 12 V I = 4.2 A
The errors in the experiment include uncertainty in the mass reading and uncertainty in reading the stopwatch, as the water boils.
Explain how another significant source of error affects the value of L obtained from the experiment.
Also involves Electrical power and energy transfers
Aluminium is one of the most widely recycled metals. Aluminium cans are heated from room temperature until all the aluminium has melted. The molten aluminium is then used to make new cans. This process uses only 5% of the energy needed to extract aluminium from raw materials.
On a website it is claimed that recycling one aluminium can of mass 14 g saves enough energy to listen to music on a mobile phone continuously for 7 days.
Assess the validity of this claim.
melting point of aluminium = 660 K specific heat capacity of aluminium = 902 J kg−1K−1 specific latent heat of aluminium = 396 kJ kg−1 room temperature = 293 K mobile phone p.d. = 3.7 V mobile phone current = 120 mA
Latte is a type of coffee made with hot frothy milk. The milk is heated by pumping steam into it.
Calculate the maximum mass of milk that could be warmed to a temperature of 65 °C by absorbing 15 g of steam at 100 °C.
initial temperature of milk = 4.0 °C specific heat capacity of milk = 3900 J kg−1K−1 specific heat capacity of water = 4200 J kg−1K−1 specific latent heat of vaporisation of water = 2.3 
106J kg−1
The apparatus shown can be used to determine a value for the specific latent heat of vaporisation of water.
In one experiment the current in the heater was 8.20 A, and the potential difference across the heater was 230 V.
Show that the power of the heater was about 2 kW.
There was 0.655 kg of water in the flask at an initial temperature of 22.5 °C. The heater was switched on, and the water in the flask was heated to boiling point.
Calculate the minimum time taken for the water to be heated to 100.0 °C.
specific heat capacity of water = 4190 J kg−1K−1
The heater was left on and water continued to boil in the flask. The water was allowed to boil for a few minutes. The conical flask was then placed under the heat exchanger and water was collected in it.
Give a reason why the water was left boiling for a few minutes before the conical flask was put in place.
Water with a mass of 95.0 g was collected in a time of 125 s.
Calculate the rate of energy transfer in the heat exchanger.
specific latent heat of vaporisation of water = 2.26 × 106J kg−1
Discuss your answers to (a)(i) and (b)(ii).
State how the apparatus could be modified to minimise the effect of a significant source of error.
A student determined the latent heat of vaporisation of a liquid using an electrical heater to boil the liquid in a Pyrex beaker.
The apparatus used is shown below.
She connected the heater into a circuit and took measurements of the potential difference V and the current I for the heater.
Complete the circuit diagram to show a suitable circuit.
The student monitored the mass of the beaker and the liquid m over the time t for which the liquid was boiling. Her results are plotted on the graph.
The student used her graph to determine a value for the latent heat of the liquid in the beaker. She concluded that the liquid was pure water.
| Liquid | Latent heat of vaporisation / MJ kg−1 |
| Pure water | 2.26 |
| Weak salt water solution | 2.10 |
| Strong salt water solution | 2.00 |
Comment on the validity of the student’s conclusion.
V = 20.5 V
I = 10.5 A
Explain how this method might be modified to improve the accuracy of the student’s conclusion.
A student determined the latent heat of vaporisation of a liquid using an electrical heater to boil the liquid in a Pyrex beaker.
The apparatus used is shown below.
She connected the heater into a circuit and took measurements of the potential difference V and the current I for the heater.
Complete the circuit diagram to show a suitable circuit.
The student monitored the mass of the beaker and the liquid m over the time t for which the liquid was boiling. Her results are plotted on the graph.
The student used her graph to determine a value for the latent heat of the liquid in the beaker. She concluded that the liquid was pure water.
| Liquid | Latent heat of vaporisation / MJ kg−1 |
| Pure water | 2.26 |
| Weak salt water solution | 2.10 |
| Strong salt water solution | 2.00 |
Comment on the validity of the student’s conclusion.
V = 20.5 V
I = 10.5 A
Explain how this method might be modified to improve the accuracy of the student’s conclusion.
Also involves Power
A student carried out an experiment to determine the specific latent heat of vaporisation of water using the apparatus shown.
glass tubing
The water in the flask was heated and steam was forced out of the flask and through the glass tubing into the cold water in the insulated cup. The steam condensed as it passed into the cold water.
The initial temperature of the cold water was 18.5°C and the mass of water in the cup was 255.0 g. After steam had been passed through the water for some time the temperature had risen to 26.0 °C and the mass of the water in the cup was 258.3 g.
Calculate the specific latent heat of vaporisation of water.
specific heat capacity of water = 4190 J kg–1 K–1
Explain why the water was heated to boiling point and left boiling for a few minutes before the insulated cup of cold water was put in place.
Identify a significant source of error in this experiment and the steps that should be taken to minimise its effect on the calculated value of the specific latent heat of vaporisation of water.
A data book contains the following information for ethanol.
latent heat of fusion = 109 kJ kg–1
latent heat of vaporisation = 838 kJ kg–1
545 J is transferred from a sample of ethanol when it condenses.
Which of the following shows how to calculate the mass of ethanol that condenses?
Memes
Laugh now. Cry in the exam hall later. Then come back and do a past paper.
Mum 💖
how's physics going sweetie?? 🥰
revising forces and motion rn
come and set the table 💖
📱 Screen time this week · TikTok6h 7m
Physics starter pack