SI units and prefixesAQA A-Level Physics: Subtopic test

1. 1
   A technician is checking the units on a data sheet for a mechanics practical involving force, pressure, energy and power.

   (a)

   Which one of the following is an SI base unit?

   [1 mark]

   • Anewton
   • Bkelvin
   • Cjoule
   • Dcoulomb

   (b)

   Which of the following gives the unit of power, the watt, in SI base units?

   [1 mark]

   • Akg m s⁻²
   • Bkg m² s⁻²
   • Ckg m s⁻³
   • Dkg m² s⁻³

   (c)

   Pressure is force per unit area. Show that the pascal can be written in SI base units as kg m⁻¹ s⁻².

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student is converting between units of energy used in two contexts: a household electricity meter, which records energy in kilowatt-hours, and a particle physics data table, which gives energies in electronvolts. Use e = 1.60×10⁻¹⁹ C.

   (a)

   How many joules are equal to 1 kW h?

   [1 mark]

   • A3.6×10⁶ J
   • B3.6×10³ J
   • C6.0×10⁴ J
   • D1.0×10³ J

   (b)

   A proton has a kinetic energy of 4.5 MeV. What is this energy in joules?

   [1 mark]

   • A7.2×10⁻²⁵ J
   • B2.8×10²⁵ J
   • C7.2×10⁻¹³ J
   • D7.2×10⁻¹⁶ J

   (c)

   A kettle of power 2.2 kW is switched on for 4.5 minutes. Calculate the energy transferred, in kW h.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A green laser pointer emits light of wavelength 532 nm with a power of 5.0 mW. Each photon from the laser has an energy of 2.33 eV. Use e = 1.60×10⁻¹⁹ C.

   (a)

   Write the wavelength in metres and the power in watts, both in standard form, and calculate the energy emitted by the laser in 60 s.

   [3 marks]

   (b)

   Calculate the number of photons emitted by the laser each second.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A science journalist compares two very different energy scales. At the Large Hadron Collider each proton in a beam has an energy of 6.8 TeV. In the home, an electric shower of power 3.0 kW is used for 8.0 minutes, and electricity costs 28 p per kW h. Use e = 1.60×10⁻¹⁹ C.

   (a)

   Show that the energy of one proton is about 1.1×10⁻⁶ J. Explain why the electronvolt, with prefixes, is more convenient than the joule in particle physics, whereas the kilowatt-hour is more convenient than the joule for household electricity.

   [6 marks]

   (b)

   Calculate the cost of using the shower for 8.0 minutes. Compare the energy transferred by the shower with the total energy of 1.0×10¹² protons from the beam, and comment on the result.

   [6 marks]

   Total for question 4: 12 marks

End of questions