O-LevelPhysicsForces5054/41 · May/June 2023 · Q46 Marks

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. [Figure 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. 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)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. [Figure 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. 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.[6]

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Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

[1] MP1 method: vary V and record the reading on balance ;
[1] MP2: five or more readings of V between 2 and 12 V ;
[1] MP3 key variables: same distance between propeller and balance ;
[1] MP4: Any one from; • same area of balance ; • same spin direction of propeller ; • same room temperature / air pressure ; • same motor ;
[1] MP5 table: columns for balance reading and voltage / p.d. / emf with units ;
[1] MP6 conclusion: plot a graph of voltage against force / mass ; or use results table to compare voltage and balance reading ; or look to see if changing the voltage changes the balance reading ;

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