Materials - AQA A-Level Physics

Density

The mass per unit volume of an object

Density unit

kgm^-3

Alloy

A mixture of two or more materials, where at least one of which is a metal.

Random

No pattern or bias

Systematic

Having a pattern or bias

Range

The difference between the minimum and maximum values in a set of repeat readings.

Precision

The closeness of the measurements.

Accuracy

The closeness to the known value.

Uncertainty

The spread of values of a measurement.

Uncertainty =

range/2

Percentage uncertainty

The absolute uncertainty expressed as a percentage of the mean measurement.

Repeatability

How easily the measurements can be taken again to the same precision and accuracy.

Reproducibility

How easily the same measurement can be repeated by another person.

How to find the uncertainty of the result of addition or subtraction of two values

Add uncertainties together

How to find the uncertainty of the result of multiplication or division of two values

Add percentage uncertainties together

How can you find the energy stored using a force-extension graph?

Find the area under the line

Hooke’s law

Force applied to an elastic object is directly proportional to extension (f=ke)

Limit of proportionality

The point beyond which behaviour no longer conforms to Hooke’s law.

Elastic limit

The point beyond which a spring will no longer return to it’s original shape once the force is removed.

What is the effective spring constant for two springs in parallel?

The sum of their individual spring constants. (k_t = k₁ + k₂)

What is the effective spring constant for two springs in series?

The reciprocal of the sum of the reciprocals of their individual spring constants. (1/k_t = 1/k₁ + 1/k₂)

Tensile stress

The force exerted per unit cross-sectional area of a material.

Tensile stress unit

Pa or GPa

Tensile strain

The extension per unit length.

Young’s modulus

The ratio of tensile strength to tensile strain and the stiffness of a material.

What will happen to a metal wire stretched beyond it’s elastic limit once it is unloaded?

The wire will have gained a permanent extension.

Elastic strain energy

The energy stored in an elastic object when it is deformed

Breaking stress

The maximum stress a material can withstand before it fractures.

Plastic behaviour

A material undergoes permanent deformation and does not return to it’s original shape when the deforming force is removed.

Brittle

Can fracture with little to no plastic deformation

Ductile

Undergoes more plastic deformation before fracture.