Download Current Electricity

Current Electricity
Chapter 51
Energy is
transferred
Chemical energy
converted to electrical
energy in battery
There is a continuous and
steady flow of charges in
all parts of the complete
circuit
An electric current
• An electric current is a flow of charge
• Conductors are substances which allow
electric current to flow through ther freely.
• Insulators are substances which do not
allow electric current to flow through them.
To show a Conductor or Insulator
If the bulb lights up
If the bulb does not light
Conductor
Insulator
Electric circuits
• A closed circuit is needed for current to
flow.
In order for a current to
flow the circuit must be
complete and there must
be a potential difference
or voltage between each
end of the circuit.
A simple circuit containing bulb,battery and switch
Misconceptions
•
•
•
•
•
•
•
Battery stores electricity
Electricity from both ends of the battery
Electricity is used up in a circuit
Battery runs out of charged particles
Battery runs out of electric current
Battery supplies all of the charged particles
Electric current gets used up in a bulb to
make it work
www.juniorscience.ie
Misconception
• Battery stores electricity
www.juniorscience.ie
Correct ideas
• Battery stores energy
• When a circuit is
complete, this energy is
released as chemical
reactions occur in the
battery, and causes a drift
of charged particles in the
circuit
Misconception
• Electricity from both ends
of the battery
www.juniorscience.ie
Correct ideas
• Electric current is in one
direction only in the
circuit
• Electrons drift away from
the negative terminal of
the battery
• The other free electrons in
the circuit drift in the
same direction
Misconception
• Electricity is used up in a
circuit
www.juniorscience.ie
Correct ideas
• Energy is transferred and
converted to other forms
of energy in the circuit
• For example, energy is
transferred and converted
in a bulb to heat and light
Misconception
• Battery runs out of
charged particles
www.juniorscience.ie
Correct ideas
• Battery runs out of energy
• There are still charged
particles in the battery, but
the chemical reactions
producing energy (and
releasing electrons) in the
battery can no longer
occur
Misconception
• Battery runs out of electric
current
www.juniorscience.ie
Correct ideas
• Battery runs out of energy
• This occurs when the
chemical reactions that
produce energy in the
battery can no longer
occur
Misconception
• Battery supplies all of the
charged particles
www.juniorscience.ie
Correct ideas
• The charged particles
originate throughout the
circuit
• Charged particles
throughout the circuit are
set in motion by the
battery when the circuit is
complete
• The charged particles are
part of the atoms that
make up the wires, battery
and bulb
Misconception
• Electric current gets
used up in a bulb to
make it work
Correct ideas
• Energy is transferred in the
bulb, and converted to heat
and light
• The current leaving the
bulb has the same value as
the current entering the
bulb, because the same
number of electrons enters
and leaves the bulb each
second
www.juniorscience.ie
Units used in Electricity
Current is the flow of electrical charge. It is
measured in Amps(A).Current (in amps) is given
the symbol (I).
Voltage, also called potential difference is the
difference in electrical pressure needed for a
current to flow.It is measured in volts (V).
Resistance is the ability of a substance to resist the
flow of electricity to flow through it. The unit of
resistance is the ohm()
Relationship between current,
voltage and resistance
The larger the voltage, the larger the current that can
flow.
The larger the resistance, the smaller the current in
the circuit.
V = I x R
I
= V/R
R = V/I
Ohm’s Law
• Ohm’s law states that the current flowing
through a metallic conductor is proportional
to the voltage across it, providing the
temperature remains constant.
To verify Ohm’s Law
In an electrical circuit, if the
voltage is increased the
current is also increased.
i.e.
Voltage =
Current
Constant
The constant for each given
conductor was later called
the resistance of the
conductor.The unit of
resistance is the ohm(Ω)
Circuit used
to
demonstrate
Ohm,s Law
Ohm’s law circuit using symbols
Plot of Voltage vs Current through the Origin
Series Circuit
• Bulbs connected in series are connected
one after the other.
• The more resistance in the circuit the less
current will flow. The more bulbs the
dimmer each one will be.
• If one bulb is disconnected the circuit is
broken
Series Circuit
Parallel Circuit
• Bulbs connected in parallel are connected side by
side
• Each bulb is connected independently of each
other. The total resistance in the circuit is much
less than in a series circuit so the bulbs are
brighter.
• If one bulb is disconnected the others continue to
light.
Parallel Circuit
The 3 effects of electric current
The three effects of electric current are:
• Heating effect
• Magnetic effect
• Chemical effect
Heating effect:
• The current has difficulty
passing through the
nichrome wire(high
resistance)
• As a result heat is given off.
Uses:
• Electric kettles, immersion
heater, electric fires, toasters
bulbs e.t.c
Magnetic effect
• When the switch is closed
a current flows.
• The compass needle turns
showing that
• there is a magnetic field
caused by the current
Uses:
• Electric motor,
electromagnet
Chemical effect
• When an electric current is
passed through water the
water is chemically broken
down into Hydrogen and
Oxygen.
• This is called the electrolysis
of water.
• The apparatus is the
Hoffman Voltameter
Electrolysis
of Water
TextbookChapter50-CurrentElectricity
A1. Current,charge.
A2. Conductors.
A3. Negative,positive,positive,negative.
A4. Potential,voltage,volts,voltmeter.
A5. Current,amps,ammeter.
A6. Resistance,ohms.
A7. Resistors,resistance.
A8. Larger.
A9. Smaller.
A10. Current,voltage,Ohm's.
A11. Series.
A12. Heating,magnetic,chemical.