SB6e Transferring energy Flashcards
Explain energy transfer due to current.
free electrons move through a lattice of vibrating positive ions. The electrons collide with the ions, transferring energy to them. The more collision, the harder it is for them to pass through and the higher the resistance. Therefore, the higher the temperature.
Why, when a current passes through a resistor, is energy being transferred?
because electrical work is being done against the resistance. The resistor becomes warm, and then this transfers energy to the surroundings (it dissipates).
State 3 advantages of the heating effect of electrical current.
.generates useful heat
.emitting light in filament lamps
.causes fuses to melt (prevents overheating)
State 2 disadvantages of the heating effect of electrical current.
.loss of energy in transmission wires
.some components work less efficiently when hot
What is resistance of a wire affected by?
.length
.diameter
.material
How can unwanted energy transfers as current flows be reduced?
.by using low resistance wires
.materials that offer very low resistance have more free electrons
What are very high resistance materials called?
insulators.
What are very low resistance materials called?
conductors.
How is resistance affected by the length of a wire?
.in a longer wire, free electrons collide with more ions in the lattice as they flow through the wire
.the increased rate of collisions make it harder for current to flow (resistance is increased)
How is resistance affected by the diameter of a wire?
.a thicker wire will have a larger diameter, so there is more space for the free electrons to pass, a lower rate of collisions with lattice ions, so resistance is lower
Why is resistance reduced by cooling wires?
ions of the lattice do not vibrate so much, hence a reduced rate of collisions by free electrons.
energy transferred = ?
current x potential difference x time
