Conservation & dissipation of energy

Some types of kettle are battery powered.

The kettle contains 0.50 kg of water at 20 C.

Calculate the minimum change in thermal energy needed to raise the temperature of the water to 100 C.

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

Use the equation:

change in thermal energy = mass specific heat capacity change in temperature

Explain why the actual amount of thermal energy needed to raise the temperature of the water would be greater than the calculated value in (a)(ii).

What is the time taken for the temperature of the water in cup B to decrease from 80 C to 60

Time taken =........ minutes

One cup is made of metal and the other cup is made of plastic.

The metal cup is a better conductor than the plastic cup.

Which cup, A or B, is made of metal?

Give a reason for your answer using information from the graph.

Suggest two variables the students should control in their experiment.

The students wrap the cups in thermal insulation and repeat the same experiment, as shown in the diagram.

Predict how these new temperature readings after 5 minutes compare to the original results on the graph.

Give a reason for your answer.

Which of these would not reduce unwanted energy transfers?

A Filling gaps around doors and window frames

B Lubricating a bicycle chain

C Increasing the temperature of your home

D Insulating a mug that contains a hot drink

In energy transfers, some energy is dissipated.

Into which store does the dissipated energy go?

A A chemical store

B A gravitational store

C A nuclear store

D A thermal store

Which sentence describes the law of conservation of energy ?

A Energy can be created in a power station.

B Energy can be transferred into power.

C Energy can only be transferred between stores.

D Energy can only be destroyed in the surroundings when it is wasted.

Which sentence describes the law of conservation of energy ?

A Energy can be created in a power station.

B Energy can be transferred into power.

C Energy can only be transferred between stores.

D Energy can only be destroyed in the surroundings when it is wasted.

Student A uses the electric hot plate in Fig. 11.1 to increase the temperature of water in a saucepan.

Fig. 11.1

Student A wants to calculate the thermal energy transferred to the saucepan of water.

These are the steps in their method:

1 Measure the volume of water with a balance. 2 Measure the starting temperature of the water with a thermometer. 3 Use the equation:

change in thermal energy = mass specific heat capacity change in temperature

Student A ’s method is incorrect.

Identify the two mistakes the student has made and write down the correction for each mistake.

Student A suggests wrapping insulation around the saucepan in Fig. 11.1.

Suggest another way student A can improve their experiment.

Student B uses the immersion heater in Fig. 11.2 to increase the temperature of water in a beaker.

Fig. 11.2

Describe an experiment to measure the energy transferred to the immersion heater, using the equipment in Fig. 11.2.

In your answer include:

• a method

• a circuit diagram

• an equation from the Data Sheet

• the symbol for a resistor to represent the immersion heater in your circuit.

This question is about energy changes in different situations.

Define braking distance.

• The braking distance is 6 m.

• The thinking distance is 6 m.

Calculate the stopping distance.

Explain how Fig. 12.1 shows the law of conservation of energy.

Complete these sentences about energy stores.

You can use each word once, more than once, or not at all.

chemical gravitational kinetic magnetic nuclear thermal

• A student rolls a ball up a hill. The ball stops at the top of the hill.

A kinetic store decreases. A........ store increases.

• A car accelerates.

A chemical store decreases. A........ store increases.

• Uranium fuel rods are used in a power station to produce electricity.

An electric kettle boils water.

A nuclear store decreases. A........ store increases.

A student measures the increase in the temperature of a metal block when it is heated.

Fig. 12.2 shows the apparatus that the student uses.

Complete the missing label on the diagram.

• The specific heat capacity of the block is 500 J / kg °C.

• The mass of the block is 0.5 kg.

• Its temperature increases by 20 °C.

Calculate the energy transferred to the block.

Use an equation from the Data Sheet to help you.

State the law of conservation of energy.

Fig. 13.1 shows the experiment a student sets up on the ground to investigate energy stores.

• The student places a magnet at the top of a small ramp.

• They place a small iron ball at the bottom of the ramp.

• The iron ball is attracted up the ramp.

• The iron ball ‘sticks’ to the magnet.

The table describes how the energy stores change.

Complete the table using the words MAXIMUM and MINIMUM.

The mass of the marble is 0.003 kg.

The kinetic energy of the marble is 0.024 J at the bottom of the ramp.

Calculate the speed of the marble at the bottom of the ramp.

Use the equation: kinetic energy = 0.5 × mass × (speed)²

Speed =........ m / s

The marble rolls to a stop on the horizontal rough surface after it leaves the ramp.

Explain what happens to the kinetic energy store of the marble.

This question is about electrical devices.

The diagram shows two different electrical devices.

Write down the source of electrical energy for each device.

torch........

Describe how energy is dissipated in the electric fan.

The electric fan is rated 230 V, 0.3 A.

Calculate the power of the electric fan.

Use the equation: power = potential difference × current

*(b) Here is a diagram of a tumble dryer and an electric drill. Each appliance is wired differently.

Explain whether the tumble dryer and electric drill are both safe to use.

Include the function of the earth, live and neutral wires in your answer.

A scientist does an experiment to measure the energy transferred to water.

She uses an immersion heater to increase the temperature of the water.

The scientist uses this apparatus:

• A beaker

• An immersion heater

• A stirring rod

• A 12 V battery and wires.

What two other pieces of apparatus does the scientist need for this experiment?

Explain how the scientist could reduce energy transfer to the surroundings.

The immersion heater is placed at the bottom of the beaker.

Suggest why.

The heater is connected to a battery. When the heater is turned on, energy is transferred.

Describe this energy transfer.

Use ideas about energy stores.

The current through the heater is 3.8 A. The potential difference across the heater is 9.0 V.

Use the equation: Power = Potential difference × Current

Calculate the power of the immersion heater.

The scientist writes down more information about her experiment.

• Mass of water = 150 g

• Specific heat capacity of water = 4200 J / kg °C

• Temperature increase of water = 10 °C

Calculate the change in thermal energy of the water.

A driver stops a moving car by pressing the brakes. The engine is turned off and the driver gets out of the car. The driver returns to the car after 30 minutes.

Which sentence is correct?

A The energy in the thermal store of the brakes increases.

B The energy in the thermal store of the driver increases.

C The energy in the thermal store of the surroundings increases.

D The energy in the thermal store of the tyres increases.