how to calculate the volts
of v3 in given circuit?
Answers
Answer:
Electrical Circuit Calculations
Series Circuits
Many circuits have more than one conversion device in them
(i.e. toaster. heater. lamps etc.) and some have more than one source of electrical energy.
If the circuit components are connected end to end to form a single loop it is a series-circuit
Remember that current is the rate at which electrons move through the circuit. So as in several hoses
connected in series to form one long line, water can only come out at the far end at the same rate that it
enters at (neglecting friction).
Each component has a volt drop across it (and is the force required to convert the electrical energy to
some other form). All of the volt drops in a circuit add up to the e.m.f. (Voltage) of the supply.
In the above circuit E = V1 + V2
(This assumes that the connecting wires have very little resistance, which is not an unreasonable
assumption to make.)
Ammeters
Ammeters are instruments that measure current and so have to be in the current path, that is, in series
with the device whose current is being measured.
The volt drop across each component can be calculated using Ohms law if the circuit current and the
value of each component's resistance is known.
(Remember that the e.m.f of the supply is across the whole circuit and not just across anyone of the
components.)
Worked Example:
• If the circuit shown draws
10 amps from the supply,
calculate the volt drop across
each resistor and the volume
of the supply e.m.f.
Note that as it is a series circuit
the current is the same in all resistors.
V1 = IR1 = 10 x 10 = 100V
V2 = IR2 = 10 x 20 = 200V
V3 = IR3 = 10 x 5 = 50V
As the volt drops all add up to the supply voltage E
E = V1 +V2 +V3
= 100+200+50
= 350v
If the supply voltage but not the
current volume had been given
in the above circuit we could
have calculated it because the
total resistance of a series
circuit Rtotal is simply the sum
of the resistances
This is the total resistance across
the supply so this circuit can
be replaced by a single resistor
of 35 ohms.
The supply current I = E/Rt
= 350/35
= 10 amps
Look at the circuit below. Even though we have connected two resistors you should be able to state
immediately what the volt drop across the two resistors together is.
The voltage drop is, of course, 24 volts.
If the supply e.m.f E and the separate resistances are given, calculate the circuit current and the volt drops
across each resistor.
1 Add the resistances to give the total resistance
2 Calculate the circuit current by dividing the supply E by RT
3 Calculate the volt drop across each resistor by using the formula:
V1 =I x R1
V2 =I x R2
V3 =I x R3 etc.
A Worked Example
• Given the circuit below calculate
I The total resistance
2 The current.
3 The volt drop across each resistor1. Total resistance: R total = R1 + R2 + R3
= 40 + 5 + 80
= 125 ohms
2. Current (I) is found by using Ohms Law: I = E/RT
= 250/125
Therefore, circuit current I = 2amps
(3) Volt drop across each resistor:
Volt drop across R1: V1 = I x R1
= 2 x 40
= 80 volts
Volt drop across R2: V2 = I x R2
= 2 x 5
= 10 volts
Volt drop across R3: V3 = I x R3
= 2 x 80
= 160 volts
As a check, the volt drops across the resistors should add up to the supply voltage.
i.e = VD1 + VD2 +VD3
= 80+10 + 160
= 250 volts.
Explanation: