Sam wants to keep his tea hot by using a USB heater under his mug.

Calculate the energy transferred to the mug by the heater in 15 minutes. 

The mug loses 4 kJ of heat to the surroundings while the mug is on the heater.

Calculate how much energy is used to heat the tea.

Calculate the final temperature of the tea after 15 minutes. 

How could the student reduce the heat lost to the surroundings?

Mary is setting up a new hot tub. When fully filled and heated it contains 1,000 litres of water at 38°C. 

The hot tub heater is rated at 3 kW.

Mary fills the hot tub with a hose pipe with water at 5°C. Once filled, she switches the heater on. 

Calculate the energy transferred to the water as it is heated from 5 °C to 38 °C.

The specific heat capacity of water is 4200 J/kg°C.

1 litre of water = 1 kg.

Calculate how long it would take for the 3 kW heater to heat the water from 5°C to 38°C. Give your answer to the nearest hour. 

Mary found it took 15.5 hours for the hot tub to reach 38°C.

Suggest why the time recorded is much higher than the calculated value.

Suggest two ways Mary might reduce the time it takes to heat the hot tub without using a different hose. 

The sun can be used to heat water inside solar heating elements. The sun transfers 1,370 J per second per square metre on the Earth's surface. 

Each solar heating element is 1.2 m long and 90 cm wide.

Calculate the area of the solar heating element.

A homeowner has 4 of these panel installed on their roof. Calculate the energy incident per second on the solar panel array. 

The array of panels contains 240 kg of water combined. Calculate the temperature change of the water when exposed to the sun for 2 hours.  

A student is investigating the properties of stearic acid. The stearic acid is heated in a boiling tube in a water bath to 90 °C. 

The student removes the boiling tube from the water bath, records the temperature and starts a timer. 

The temperature is recorded every 10 s for 150 s.

Plot a graph of time against temperature for the student's results. 

The graph plotted is a line graph.

Explain why a line graph more appropriate than a bar chart for temperature data.

Using the graph, identify the freezing point of stearic acid.

Describe what happens to the arrangement and motion of the particles within the acid as it freezes.

The mass of stearic acid used was 50 g and the specific heat capacity of stearic acid is 2,300 J/kg°C. 

Calculate the energy transferred between 0 s and 30 s.

A student is investigating the specific heat capacity of an unknown liquid. 

Their method is below:

1. Record the mass of the liquid using a top pan balance.
2. Record the initial temperature of the liquid using a thermometer. 
3. Turn on the heater and start the timer. 
4. Record the voltmeter and ammeter readings.
5. After 10 minutes have elapsed, turn off the heater and record the temperature. 
6. Calculate the temperature difference by subtracting the initial temperature from the final temperature.
7. Calculate the energy transferred to the liquid by using the equation E = VIt.
8. Calculate the specific heat capacity of the liquid using: 

Using the data from the table, calculate the mass of the unknown liquid.

In step 4 of the student's method, the heater is turned off and the temperature recorded.

Explain why is this incorrect.

The current through the circuit was 3 A. 

Calculate the energy transferred by the 12 V heater during the 10 minutes it was turned on.

During the experiment the student recorded an initial temperature of 22^oC and a final temperature of 45^oC.

Calculate the temperature change and the hence determine the specific heat capacity of the unknown liquid. 

State the name of the material the liquid is likely to be made from.

Explain why the calculated value of specific heat capacity is different to the accepted value. You should refer to the student's method in your answer. 

A piece of iron of mass 4.5 kg is heated in a furnace to 1,250°C before being plunged into a bath of cold water containing 20 kg of water at 5^°C. The specific heat capacity of iron is 451 J/kg°C. 

The iron will cool when placed in the water bath. Eventually the iron bar will be in thermal equilibrium with the water. Describe what is meant by thermal equilibrium.

The iron bar is heated from room temperature at 22°C up to 1,250°C. The specific heat capacity of iron is 451 J/kg°C. 

Calculate the amount of energy required to heat the iron bar.

When a larger piece of iron is placed in the water bath, some of the water boils. 

Describe what happens to the internal energy, and the kinetic and potential energy stores of the water, as it boils.