Use of SI Units & Their Prefixes (AQA AS Physics)

Use the equation Capacitance =    to write 1 Farad [F] in SI base units.

A parallel plate capacitor of capacitance 75μF is connected to a 5 kV power supply.

Using the equation Charge = Potential difference × Capacitance, calculate the charge between the plates in mC.

Write the following capacitance in order of increasing magnitude:

             1 pF, 1 µF, 1 cF, 1 fF

Estimate the current through an 1800 W kettle connected to a UK mains supply using the equation Power = Potential difference × Current 

Convert the following measurements into standard form.

   40000 kJ = ________________ J

   0.23 GW = _______________ W

   1.15 fm = ______________ m

   72.6 pC = _______________ C

X-rays from a pulsar travel at the speed of light and are detected on earth with a wavelength of 5 nm. 

Using an appropriate equation, calculate the frequency of the X-rays in THz.

X-rays from the nearest pulsar PSR J0109-1431 take 8.82 Gs to travel to Earth. 

Show the distance from Earth to PSR J0109-1431 is around 280 light years.

Use the hydrostatic pressure equation to write 1 Pascal [Pa] in SI base units.

A box is placed on the floor. The area of the box in contact with the floor is 4.9 cm². The pressure exerted on the floor is 20 kPa. 

Using the equation linking Pressure, Force and Area, calculate the force exerted by the box on the floor. 

Atmospheric pressure on Earth is 101 325 Pa. The Mariana trench at the bottom of the western Pacific Ocean has a pressure of around 110 MPa.

Write the following in order of decreasing pressure:

• Atmospheric pressure at the summit of Mount Everest
• Surface pressure on the Moon
• Atmospheric pressure ~ 101 kPa
• Water pressure of an average garden hose
• The Mariana trench ~ 110 MPa

Use the equation linking Power, Current and Potential difference to write 1 Watt [W] in SI base units.

Kilowatt-hour (kWh) is a unit of energy.

Convert your answer from part (b) into MJ.

A 5.1 kW hair dryer is used for 45 minutes. The electricity bill is charged as 8 p per kWh used.

Use the equation linking Force, Momentum and Time to write 1 Newton in SI units.

To leave Earth, a rocket must travel at around 8 km s^–1.

Calculate the thrust on a rocket which ejects 2.3 × 10⁴ kg of waste gas per second to leave Earth in MN. Show all your working clearly.

A rocket can hold 20 000 kg of material.

Estimate the impulse on a tennis ball travelling at 70 m s^–1 as it hits a racket.

The Tesla, symbol T, is the unit of magnetic flux density.

Complete Table 1 by converting the following measurements into their appropriate SI unit and express to an appropriate number of significant figures.

Table 1

1 eV is the amount of kinetic energy gained by a single electron accelerating from rest through a potential difference of 1 V.

1 eV = 1.60 × 10^-19 J.

Convert the following measurements to the appropriate unit, and express to an appropriate number of significant figures.

   60000 GW = ____________ MW

   25.8 µF = _____________ pF

   0.19 fm = _____________ km

   416 minutes = ____________ms

A sheet of silver has a thickness of 0.671 µm. A silver atom has a radius of 172 pm.

A silver block of volume 0.67 cm³ is used to a make a silver ring of mass 7 g. 

Tensile stress (σ) is defined as the force applied per unit cross-sectional area on a material. The tensile strength is the maximum amount of tensile stress a material can be subjected to before fracturing. 

The humerus bone is approximately cylindrical and has a tensile strength of 0.17 GPa and a diameter of 20 mm. 

The femur bone is the strongest bone in the body. It has a tensile strength of 0.135 kN mm^–2.

Calculate the number of cubic millimetres (mm³) in 15 km³

The distance time graph for a lorry travelling at constant speed is shown in Figure 1.

The velocity-time graph of a different lorry is shown in Figure 2.

Calculate the acceleration of the lorry in Figure 2 into the appropriate SI unit.

Estimate the order of magnitude with an appropriate SI unit and correct prefix for the following quantities in Table 1. 

Table 1

The equation Energy = Mass × (Speed of light)²­ demonstrates that energy and matter are interchangeable.

 1 u is the atomic mass unit and a common unit used in nuclear physics.

 1 u is equal to 931.5 MeV, where 1 eV= 1.60 × 10^-19 J ^.

Show that its value in kg is approximately equal to the mass of a proton in kg.

The cross-sectional area of nuclei is commonly measured in units of ‘barn’, symbol b.

 1 barn = 100 fm²