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

The average kinetic energy E of a gas molecule is given by the equation

E =  kT 

where T is the absolute (Kelvin) temperature.

What are the SI base units of k?

The units of all physical quantities can be expressed in terms of SI base units.

Which pair contains quantities with the same base units?

The table contains some quantities, together with their symbols and units.

Which expression has the units of energy?

For which quantity is the magnitude a reasonable estimate?

2.5 kilowatt-hours (kW h) is equivalent to

Which of the following correctly expresses the Ohm in terms of SI base units?

Which one of the following cannot be used as a unit for electric field strength?

The equation of hydrostatic pressure relates the pressure of a fluid, P, to the density of the fluid, ρ, and is given by

P = ρgΔh

Where g is the gravitational field strength, and Δh is the depth from the surface of the fluid.

How can both sides of this equation be written in terms of base units?

The units of all physical quantities can be expressed in terms of SI base units.

Which pair contains quantities with different base units?

Which of the following would be the most reasonable estimate for the energy of a photon of violet light?

Which formula could be correct for the speed v of ocean waves in terms of the density ρ of sea-water, the acceleration of free fall g, the height h of the wave and the wavelength λ?

The drag coefficient C_d is a number with no units. It is used to compare the drag on different cars at different speeds. It is given by the equation

 C_d = 

 where F is the drag force on the car, ρ is the density of the air, A is the cross-sectional area of the car and v is the speed of the car.

 What is the value of n?

When a constant braking force is applied to a vehicle moving at speed v, the distance d moved by the vehicle as it comes to rest is given by the expression

d = kv²

where k is a constant.

When d is measured in metres and v is measured in metres per second, the constant has a value of k₁.

What is the value of the constant when the distance is measured in metres, and the speed is measured in kilometres per hour?

The frictional force F on a sphere falling through a fluid is given by the formula

F =  

where a is the radius of the sphere, η is a constant relating to the fluid and v is the velocity of the sphere.

What are the units of η?

The speed v of a liquid leaving a tube depends on the change in pressure ΔP and the density ρ of the liquid. The speed is given by the equation

v = k

where k is a constant that has no units.

What is the value of n?

Which estimate is realistic?

The theory of gas flow through small diameter tubes at low pressures is an important consideration of high vacuum techniques.

One equation used in this theory is

Q =

Where k is a unitless constant, r is the radius of the tube, p₁ and p₂ are the pressures at each end of the tube, L is the length of the tube, M is the molar mass of the gas, R is the molar gas constant and T is the thermodynamic temperature of the gas.

What are the base units of Q?

The conductivity of a metal is determined by how many free electrons it contains. The densities and relative atomic mass of four different metals is shown below.

Which row shows the correct order of the metals, from best thermal conductor to worst?

 You may take Avogadro's number to be 6.02 × 10²³ mol⁻¹ and you can assume each metal contributes one free electron per atom.

Each binary digit on a computer is called a bit. A series of eight bits forms a byte (B). A CD-ROM holds 650 megabytes (MB) of information.

A typical book contains 200 pages or 240 000 characters.

If each character is equal to 1 byte, how many books can be stored on the CD-ROM?

Which of the following is the best estimate for the mass of the Earth’s atmosphere?

You may take Earth’s atmospheric pressure to be 1 × 10⁵ Pa