Physics Chapter 5 Flashcards
State the Coulomb’s law.
The electric force between two point charges is directly proportional to the product of their magnitudes and inversely proportional to the square of their separation.
F=kQq/r^2
Define electric field.
Electric field strength is the electric force per unit charge acting on a small point positive test charge.
Explain why electric field lines can never touch or cross. [2]
An electric field line gives the direction of motion of a positive charge/ the direction of electric force acting on a positive charge. [1]
If the lines cross, it means that the positive charge would move in two directions at the same time which is impossible. [1]
Define electrical resistance, R
Electrical resistance is the potential difference (NOT voltage) across the wire over the current passing through the wire.
Define electromotive force (e.m.f)
The work done per unit charge supplied by a cell which drives it completely around a circuit.
Suggest why the average speed of electrons does not keep increasing even though it is accelerated by an electric field.
Electrons accelerated by an electric field move at an increasing speed until they collide with lattice atoms.
Then, some of their kinetic energy is transferred to the atom, and they slow down.
However, then they are accelerated by the electric field again
Eventually, the electrons reach a steady speed, and this is called drift velocity
Explain, in terms of electrons, what happens to the resistance of a conductor as the temperature of the
conductor increases. [4]
When the temperature of the conductor increases,
the metal atoms vibrate more quickly. [1]
The collisions between the free electrons and the atoms become more frequent. [1]
The drift velocity of the electrons decreases. [1]
As a result, the resistance of the conductor increases. [1]
State Ohm’s law.
It states the potential difference across a material is directly proportional to the current through it provided that the temperature remains unchanged.
Suggest why there must be an electric field inside a current-carrying conductor
To have the free electrons moving along a conductor, [1]
there must be electric force acting on the electrons. [1]
The force is provided by the electric field. [1]
State what is meant by conduction electrons.
They are delocalized electrons are not bound to any particular atoms of the metal.
Outline what is meant by the internal resistance of a cell. [2]
It is resistance of the chemicals within the cell [1]
that causes energy loss in it. [1]
