F3 C6 direct current and alternating current

Hydroelectric power station (hydro energy)

Energy change

Gravitational potential ➡ kinetic energy ➡ electrical energy

Biomass energy

Chemical energy ➡ heat energy ➡ kinetic energy ➡ electrical energy

Thermal power station (Diesel, natural gas or coal)

Chemical energy ➡ heat energy ➡ kinetic energy ➡ electrical energy

Nuclear energy- power station

Nuclear energy ➡ heat energy ➡ kinetic energy ➡ electrical energy

Direct current (d.c.)

An electric current that flows in one direction only such as,

• Calculator

• Torchlight

• Wrist watch

Source: batteries, solar cells, accumulators

Alternating current (a.c.)

An electric current that flows in constantly reversing directions such as,

• Iron

• Bread toaster

• Hair dryer

Source: generator, power station

Step-up transformer

• Increases the voltage of alternating current

• Number of turns of the primary coil, N(p) is less than the number of turns in the secondary coil, N(s)

• Primary voltage, Vp (input) is lower than the secondary voltage, Vs (output)

• The output of alternating current is smaller than the input current.

Step-down transformer

• Decreases the voltage of alternating current

• Number of turns of the primary coil, N(p) is more than the number of turns in the secondary coil, N(s)

• Primary voltage, Vp (input) is higher than the secondary voltage, Vs (output)

• The output of alternating current is larger than the input current.

Gravitational potential energy

Energy possessed by an object with a mass due to its position on the surface of the earth such as,

• Rock on the hillside

• Parachuting activity

• Skateboarding

Formula of gravitational potential energy

Gravitational potential energy = mgh

• m = mass of object in kg

• g = gravitational acceleration in m s–²

• h = height in m

Elastic potential energy

Energy possessed when an object is stretched, compressed and bent such as,

• Arrows being pulled

• Spring is stretched and compressed

• A boy jumping on a trampoline

Formula elastic potential energy

Elastic potential energy = ½Fx,

• F = stretching or compression force in M

• x = displacement from the equilibrium position in m

Kinetic energy

Energy possessed by a moving object such as,

• Cycling

• Pushing a stroller

• A moving toy car

• A spinning fan

Formula kinetic energy

Kinetic energy = ½mv²

• m is mass in kg

• v is velocity in m s–¹