CURRENT ELECTRICITY
CURRENT ELECTRICITY
Current electricity is the rate at which an electricity source will make charges to flow or pass a certain point in a conductor or in an electric circuit.
This means that, when electrical devices are joined in an electric circuit, electrons flow in a continuous path. It is the flow rate of which is referred to as current electricity or electric current.
Current electricity is the rate at which an electricity source will make charges to flow or pass a certain point in a conductor or in an electric circuit.
This means that, when electrical devices are joined in an electric circuit, electrons flow in a continuous path. It is the flow rate of which is referred to as current electricity or electric current.
The sources of electricity are of
different nature which include;
- Generators
- Charged capacitors
- Dry cells
- Dynamo
- Solar panels
The device in which energy
transformation occurs and is maintained is called electrical source.
Load - is the device used for transforming the electrical energy
into any of the sensible forms of energy.for example; heat, light, mechanical
or sound energy etc.
The quantity of electricity is
measured in coulombs denoted by 'C'.
It follows that, if the quantity of charge of 6 coulombs is passed at a certain point of a conductor in 3 seconds, then;
It follows that, if the quantity of charge of 6 coulombs is passed at a certain point of a conductor in 3 seconds, then;
Electric current = 2 coulombs/second or 2C/s
SIMPLE ELECTRIC CIRCUITS
Electric circuit - is a continuous path formed by connecting electrical
devices. Such as Battery, switch, socket etc along which electrons can flow.
A simple electric circuit may
consist of;
- Cell or any source of current electricity.
- Switch or control to allow or restrict the flow of
current electricity.
- Conductor to transmit the current electricity.
- Load to consume the supplied power delivered by the
current electricity.
The figure below shows the simple
electric circuit containing a sound (cell), a control (switch) and the load
(bulb);
The electric devices used in a
circuit are called circuit, components or elements.
USES OF COMPONENTS OF ELECTRIC CIRCUIT
- Cell or battery
– Is a source of electric current.
- Switch
– Is a device used to switch on an electric current in order to allow the
flow of an electric current or off an electric current thus to stop the
flow of the electric current respectively.
- Resistor
– Is a component included in an electric circuit because of its resistance
to current electricity flow. There are variable value resistors and
fixed value resistors, all are made of resistance wire or carbon.
- Ammeter
– Is an instrument with low internal resistance used for measuring
electric current.
- Connecting wire
– Is a material used to provide a direct path which allows the flow of
current between two points in a circuit and are used to connect circuit
components.
- Capacitor
– Is an electric conductor or a system of electrical conductors which can
store electric charge.
- Voltmeter
– Is an instrument with high internal resistance used for measuring
potential difference of any two points in an electric circuit.
- Socket and plugs
– Are devices that connect electrical appliances to the power supply so
that electric power can flow through them.
CONCEPT OF CURRENT, VOLTAGE AND
RESISTANCE IN AN ELECTRIC CIRCUIT
The electric current flows
from a point with low potential to the point with high potential.
The S.I unit of electric current is Ampere
denoted by ‘A’. The electric current (I)encounters resistance (R)
along its path, which will result in voltage drop (V) in a circuit.
The S.I unit of resistance is Ohms
denoted as Ω.
The potential difference (P.d)
which causes electric current to flow is defined as “the energy per coulomb
consumed when electricity moves from one point to another”.
The S.I unit of potential difference
is volt (V). This voltage is given as the product of current flowing
between two points and resistance offered between the two points
I.e.
Voltage = Current In amperes X Resistance in Ohms
V = I x R
V =
IR
OHM’S LAW
-It states that “the voltage across
the conductor is directly proportional to the electric current flowing if
temperature is constant”
The resultants shows that the
resistance of a wire (P.d) is proportional to the current flowing through the
conductor
I.e. Vα I
Introducing proportionality constant
‘K’
V = KI
The constant of proportionality is
called the resistance ‘R’ thus,
V = IR
COMBINATION OF RESISTORS
Resistors can be connected either in
series or parallel depending on the magnitude of effective
resistance required. Series connection gives a bigger value of effective
resistance and the parallel connection gives small value of effective
resistance.
RESISTORS IN SERIES
By connecting resistors in series,
when the switch 'S' is closed, the current 'I' which flows
through the circuit flows through each resistor.
Total resistance between points A
and B which is commonly referred to as equivalent resistance (Req)
will produce a potential difference in the circuit given by ohm’s law as;
V=IReq
The voltage across each resistor in
the circuit is given by V1 =IR1 and V2 =IR2
The sum of the voltage drops equal
to the potential difference in the circuit (i.e. potential difference between
(A and B)
Total voltage = V1 + V2
... VT
= V1 + V2
Total voltage = V1 + V2
Since V = IR, V1 = IR1
and V2 = IR2
IRT = IR1 + IR2
IRT =I (R1 + R2
)
RT = R1 + R2
RESISTORS IN PARALLEL
RESISTORS IN PARALLEL
In the figure below I is the current
in the main circuit. On the other hand I1 and I2 are
current through individual resistors R1 and R2.
The sum of all currents through the
resistors which are connected in parallel gives the value of current equal to
the main circuit.
.
.
Therefore, IT = I1
+ I2
If RT is the equivalent
resistance of the main circuit between A and B, then by Ohm’s law the current
is given by;
From IT = I1 +
I2
On diving both sides by V
On diving both sides by V
Cross multiplication
1(R1R2) = RT
(R1 + R2)
For two resistors connected in
parallel.
EXAMPLES
1.Given that R1= 4Ω and R2= 6Ω, find the equivalent resistance when the resistors are connected.
1.Given that R1= 4Ω and R2= 6Ω, find the equivalent resistance when the resistors are connected.
- In parallel
2.
In series
Solution
1.Series
Solution
1.Series
RT = R1+R2
RT = 4Ω + 6Ω
RT = 10Ω
2.Parallel
2.Parallel
= 2.4Ω
2.Two conductors of resistance 4Ω and 5Ω are connected in series across a 60V supply. Find;
2.Two conductors of resistance 4Ω and 5Ω are connected in series across a 60V supply. Find;
- The total resistance
- The current in the circuit
- The potential difference across each resistor
RT = R1+R2
= 4Ω + 5Ω
= 9Ω
the total resistance = 9Ω
the total resistance = 9Ω
I = 6.7A
Potential difference across R1
Potential difference across R1
V1 = IR1
V1 = 6.7 x 4 = 26.8v
Potential difference across R2
V2 = IR2
V2 = 6.7 x 5 = 33.5v
Total current = 26.8 + 33.5 = 60A
3.Consider the circuit shown below.
What will be the reading on the Ammeter?
Solution
V = 12V
RT =2Ω
I = 6A
EXERCISE
1. In a circuit, the amount of charges passing through a point is 9 coulombs in 4.5 seconds. What is the electric current passing at that point?
1. In a circuit, the amount of charges passing through a point is 9 coulombs in 4.5 seconds. What is the electric current passing at that point?
Solution
Quantity of charges = 9 coulombs
Time = 4.5 sec
Electric current =?
Electric current = 2coulombs/sec
2. The two resistances 15Ω and 5Ω are connected in series across 20v supply, find;
2. The two resistances 15Ω and 5Ω are connected in series across 20v supply, find;
- Total resistance
- The total current in the circuit
- The current through each resistor
Solution
Data given
R1 = 15Ω
R2 = 5Ω
Voltage = 20v
The total resistance
The total resistance
RT = R1 + R2
= 15Ω + 5Ω
= 20Ω
The total current in a circuit (I)
The total current in a circuit (I)
From V = IR
But v = 20v, R = 20Ω
I = 1A
The current through each resistor
But V = 20V, R1 =15Ω
= 1.3A
but V = 20 V, R = 5Ω
but V = 20 V, R = 5Ω
I2 = 4A
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