Planning Experiments and Investigations

When a table tennis ball is dropped as shown in Fig. 4.1, it will bounce back upwards. Some of the initial gravitational potential energy (GPE) of the ball is lost in the bounce.

Plan an experiment to investigate how the height from which the ball is dropped affects the percentage of GPE lost in each bounce.

You may use any apparatus commonly found in a school laboratory in addition to the apparatus shown in Fig. 4.1.

GPE is given by the equation:

$$\text{GPE} = mgh$$

where $m$ is the mass of the ball, $g$ is the gravitational field strength and $h$ is the height above the bench from which the ball is dropped.

You are not required to do this experiment.

In your plan, you should:

• state what you will measure (dependent variable) and any additional apparatus you may use
• state any key variables to keep constant
• explain how you will ensure the results are as accurate as possible
• draw a table with column headings to display the results
• explain how you will use the results to draw a conclusion.

As a metal ball falls through a liquid, it experiences a frictional force from the liquid that opposes the motion of the metal ball.

Plan an experiment to determine the relationship between the density of a liquid contained in a measuring cylinder and the average speed of a metal ball falling through the liquid from the surface of the liquid to the bottom of the cylinder.

The average speed of the ball is calculated using the equation:

$$\text{average speed} = \frac{\text{distance travelled}}{\text{time taken}}$$

The arrangement of the apparatus is shown in Fig. 4.1.

The apparatus available includes:

• a measuring cylinder
• a metal ball
• a selection of different liquids whose densities are known.

You are not required to do this experiment.

In your plan include:

• any other apparatus needed
• a brief description of the method, including what you will measure and how you make sure that your measurements are accurate
• the variables you will control
• a results table to record your measurements (you are not required to enter any readings in the table)
• how you will process your results to draw a conclusion.

A solar cell is a device that can generate electrical power when light falls on it.

You are given a solar cell connected to a fixed resistor as in the incomplete circuit shown in Fig. 4.1.

Plan an experiment to investigate how the brightness of the light falling on the solar cell affects the electrical power output of the solar cell.

The power of the cell can be found using the equation shown.

$$\text{power} = \text{current} \times \text{voltage}$$

The following apparatus is available in addition to the apparatus shown in the circuit diagram:

• a lamp connected to a power supply
• a metre rule
• a voltmeter
• an ammeter
• connecting leads.

Other apparatus normally available in a school laboratory can also be used.

You are not required to do this experiment.

In your plan, you should:

• explain how you will vary the brightness of the light falling on the solar cell
• show how the voltmeter and ammeter are used. You may draw on Fig. 4.1 to help your explanation
• state any variable(s) that you will control
• draw a table with column headings to show how to display recorded measurements (you are not required to enter any readings in the table)
• explain how to use your measurements to reach a conclusion.

A student investigates the rate of cooling of hot water in a beaker.

Plan an experiment to investigate the relationship between the thickness of the cardboard insulation wrapped around the beaker and the rate of cooling of the hot water in the beaker.

The apparatus available includes:

• a supply of hot water
• a beaker
• a thermometer
• a supply of 1 mm thick cardboard sheets.

You are not required to do this experiment.

In your plan include:

• any other apparatus needed
• a brief description of the method, including what you will measure and how you make sure that your measurements are accurate
• the variables you will control
• a results table to record your measurements (you are not required to enter any readings in the table)
• how you will process your results to reach a conclusion.

Plan an experiment to investigate how the thickness of a metal wire affects its resistance.

The resistance of a wire can be found using the equation:

$$\text{resistance of wire} = \frac{\text{potential difference (p.d.) across wire}}{\text{current in the wire}}$$

The following apparatus is available:

• six lengths of metal wire, each of different thickness
• an ammeter
• a voltmeter
• a power supply
• several connecting leads
• a micrometer.

Other apparatus normally available in a school laboratory can also be used.

You are not required to do this experiment.

In your plan, you should:

• draw a circuit diagram to show how you will use the apparatus
• explain briefly how to carry out the investigation
• state the key variables to keep constant
• draw a table, with column headings, to show how to display readings (you are not required to enter any readings in the table)
• explain how to use these readings to reach a conclusion.

A student has a converging (convex) lens and needs to determine its focal length.

Plan an experiment that will enable the student to measure an accurate value for the focal length $f$ of the lens.

The focal length $f$ of a lens can be calculated using the equation:

$$f = \frac{uv}{u + v}$$

where $u$ is the distance between an object and the lens and $v$ is the distance between the focussed image of the object and the lens.

Fig. 4.1 shows some of the apparatus available.

The lamp is connected to a power supply and can be switched on and off as required.

Write a plan for the experiment.

You are not required to do this experiment.

In your plan you should:

• list any additional apparatus needed
• draw a diagram of the arrangement of the apparatus, labelling $u$ and $v$
• explain briefly how to do the experiment
• state the steps taken to obtain a sharp, focussed image
• explain how to use your readings to determine $f$.

A student uses ice cubes to investigate the time taken for different masses of ice to melt when the ice cubes are placed in water.

Plan an experiment using ice cubes to investigate how the mass of ice affects the time taken for the ice to melt.

You are not required to do this experiment.

The following apparatus is available:

• top pan balance
• supply of ice cubes
• 250 $\text{cm}^3$ beaker
• supply of cold water
• stopwatch.

You may also use other apparatus and materials that are usually available in a school laboratory.

In your plan, you should:

• explain briefly how to do the investigation
• state the key variables to keep constant
• draw a table, with column headings, to show how to display readings (you are not required to enter any readings in the table)
• explain how to use these readings to reach a conclusion.

You do not have to include a diagram of the apparatus you use but you may do so if it helps your plan.

Water is heated from room temperature to its boiling temperature in a glass beaker.

Plan an experiment to investigate if the time taken for the water to reach its boiling temperature depends on the diameter of the water surface exposed to the air.

You are provided with:

• a supply of cold water
• a set of glass beakers of different sizes
• a Bunsen burner, tripod and gauze
• a measuring cylinder.

You may use any other common laboratory apparatus.

You are not required to do this investigation.

In your plan include:

• any other apparatus needed
• a brief description of the method, including what you will measure and how you will make sure your measurements are accurate
• the variables you will control
• a results table to record your measurements (you are not required to enter any readings in the table)
• how you will process your results to draw a conclusion.

You may include a labelled diagram if you wish.

A student attaches a propeller to an electric motor driven by a 0 to 12 V d.c. power supply as shown in Fig. 4.1.

Moving air from the propeller exerts a force on the balance.

Plan an experiment to investigate how this force varies with the voltage of the power supply.

The following apparatus is available:

• an electric motor
• an electronic balance
• a power supply
• a propeller
• a voltmeter.

You can also use other apparatus and materials that are usually available in a school laboratory.

You are not required to do this investigation.

In your plan, you should:

• explain briefly how to carry out the investigation
• state the key variables to control
• draw a table, with column headings, to show how to display your readings (you are not required to enter any readings in the table)
• explain how to use your readings to reach a conclusion.

A student investigates the time taken for ice cubes to melt when they are placed in a beaker of hot water.

Plan an experiment to investigate how the thickness of the cardboard insulation around a beaker affects the time taken for the ice cubes in the beaker to melt.

You are not required to do this experiment.

The following apparatus is available:

• 250 $\text{cm}^3$ beaker
• supply of hot water
• supply of ice cubes
• thermometer
• stopwatch
• supply of 2 $\text{mm}$ thick cardboard sheets.

In your plan you should:

• explain briefly how to carry out the investigation
• state the key variables to keep constant
• draw a table with column headings to show how to display the readings
• explain how to use your readings to reach a conclusion.