jwpn 3.3

• Potential difference across the nichrome wire
increases as current increases.

• Potential, V is directly proportional to current, I

MOZAC

• From the graph, I = 0, V = 3.0 V
• Therefore, e.m.f, E = 3.0 V

MOZAC

Explain Internal Resistance, r

• The internal resistance, r of a source or battery is the resistance
against the moving charge due to the electrolyte in the source or
cell.

• Work is needed to drive a charge against the internal resistance.
• This causes a drop in potential difference across the cell as the

charge flows through it and loss of heat energy in the cell.

MOZAC

A standard dry cell battery is made • Chemical reaction within the
up of: battery cause electrons to be
stripped away from the carbon
• A zinc case rod electrode.
• A carbon rod
• Electrolyte – ammonium chloride • These electros will flow through
the electrolyte to be collected on
jelly. the zinc case, which acts as the
negative terminal.
MOZAC

• The carbon rod • Electrons will flow from the negative terminal of the
consist of atoms battery to the positive terminal through a wire in a
with shortage of complete circuit.
electrons and
therefore act as the • The force to move electron around a circuit is called
positive terminal the electromotive force, emf.

MOZAC

• The rate of flow and production of • A car battery which is also known
electrons within the battery depends on a lead acid accumulator has a
the material that made up the electrode smaller internal resistance than
and the electrolyte. the dry cell.

• Electrolyte opposes the flow of electrons • The electrodes of the car battery
in a battery. are made up of metals with large
surface area and placed in the
• Hence a battery has internal resistance. electrolyte.

MOZAC

MOZAC