Energy and fields

Track H1 Physics energy stores and transfers, calculate work and potential energy, and solve power and efficiency problems.

GCE A-Level H1 Physics 2027
4 lessons

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Before you begin

Energy is never created or destroyed, only stored and transferred, and work is how a force transfers it. The lessons start with energy stores, work and kinetic energy, then introduce gravitational and electric fields and the potential energy that goes with them, show how elastic energy is found from a force–extension graph, and finish with power and efficiency.

Be comfortable with: Newton’s laws, because the kinetic energy equation comes from F = ma and the equations of motion.

Learning goals

Track energy stores and transfers, then apply conservation of energy.
Define work and derive and apply the kinetic-energy relationship.
Derive Eₖ = ½mv² from the definition of work done by a force and the uniformly accelerated motion equations.
Represent fields and relate work done by a field to potential-energy change.
Draw field-line representations of uniform and radial gravitational and electric fields.
Use force–extension graphs to determine elastic potential energy.
Apply power, mechanical power and efficiency relationships.

Syllabus statements covered

show an understanding that physical systems can store energy, and that energy can be transferred from one store to another
give examples of different energy stores and energy transfers, and apply the principle of conservation of energy to solve problems
show an understanding that work is a mechanical transfer of energy, and define and use work done by a force as the product of the force and displacement in the direction of the force
derive, from the definition of work done by a force and the equations for uniformly accelerated motion in a straight line, the equation Eₖ = ½mv²
recall and use the equation Eₖ = ½mv² to solve problems
show an understanding of the concept of a field as a region of space in which bodies may experience a force associated with the field
define gravitational field strength at a point as the gravitational force per unit mass on a mass placed at that point, and define electric field strength at a point as the electric force per unit charge on a positive charge placed at that point
represent gravitational fields and electric fields by means of field lines (e.g. for uniform and radial field patterns)
show an understanding that the force on a mass in a gravitational field (or the force on a charge in an electric field) acts along the field lines, and the work done by the field in moving the mass (or charge) is equal to the negative of the change in potential energy
distinguish between gravitational potential energy, electric potential energy and elastic potential energy
recall that the elastic potential energy stored in a deformed material is given by the area under its force-extension graph and use this to solve problems
define power as the rate of energy transfer
show an understanding that mechanical power is the product of a force and velocity in the direction of the force
show an appreciation for the implications of energy losses in practical devices, and solve problems using the concept of efficiency of an energy transfer as the ratio of useful energy output to total energy input

Lessons

Work through them in order.

Practise and check

Or choose

Topic reference

Quick reference

Idea	Relationship	Note
work done by a force	W = Fs cos θ	θ between the force and the displacement
kinetic energy	Eₖ = (1/2)mv²	total work done = Δ Eₖ
gravitational field strength	g = F/m	N kg⁻¹
electric field strength	E = F/Q	N C⁻¹; force on a positive charge
field and potential energy	W_field = -Δ Eₚ	positive field work lowers potential energy
elastic potential energy	area under the force–extension graph; (1/2)Fx for a Hooke’s law spring
power	P = W/t, P = Fv	1 W = 1 J s⁻¹
efficiency	(useful output)/(total input) × 100%	always less than 100%

Core knowledge to remember

Energy can be stored in a system and transferred from one store to another. It is conserved: it cannot be created or destroyed.
Work is a mechanical transfer of energy: the work done by a force is the product of the force and the displacement in the direction of the force.
A field is a region of space in which bodies may experience a force associated with the field.
Gravitational field strength at a point is the gravitational force per unit mass on a mass placed at that point. Electric field strength at a point is the electric force per unit charge on a positive charge placed at that point.
The force on a mass in a gravitational field, or on a charge in an electric field, acts along the field lines. The work done by the field in moving the mass or charge is equal to the negative of the change in potential energy.
The elastic potential energy stored in a deformed material is given by the area under its force–extension graph.
Power is the rate of energy transfer. Mechanical power is the product of a force and the velocity in the direction of the force.
Efficiency is the ratio of useful energy output to total energy input.

Common mistakes

Saying friction destroys energy. It transfers energy to internal energy.
Using W = Fs when the force is at an angle to the motion.
Thinking positive work by a field increases potential energy.
Saying the electric field points the way an electron is pushed.
Multiplying the final force by the extension instead of finding the area under the force–extension graph.
Dividing useful output by wasted output when calculating efficiency.