Calculations on Voltage

Volt

Voltage = energy ÷ charge                           V = E/Q                 1 Volt = 1 Joule / 1 Coulomb

1.       Calculate the voltage across a bulb if 20 C transfers 4 J of electrical energy. Draw an energy transfer diagram.

V = 4 J ÷ 20 C = 0.2 V                        electrical à light + thermal

2.       Calculate the voltage across a dynamo if 600 J of energy is transferred by 25 C of charge. Draw an energy transfer diagram. (How is it different from q1?)

V = 600 J ÷ 25 C = 24 V                    kinetic à electrical + heat             

here another form of energy is transferred to electrical wheras in q1 energy is transferred from electrical to other forms

3.       A bulb has a voltage of 6V across it. Calculate the energy is transferred by 90 C.

E = V x Q = 6 V x 90 C = 540 J

4.       A train motor operates on a voltage of 25 kV (1kV = 1000 V). Calculate the charge that transfers    800 kJ (1kJ = 1000 J) of electrical energy.

Q = E ÷ V = 800000 J ÷ 25000 V = 32 C

5.       A torch bulb runs off a 1.5V cell (battery). Calculate the energy transferred by a charge of 0.27 C

E = V x Q = 1.5 V x 0.27 C = 5.56 J

6.       A bulb takes a current of 0.25 A. How many Coulombs per second? 0.25 C per second.

It transfers 60W of power. How many Joules per second? 20 J per second

Calculate the voltage of the supply. V = E ÷ Q = 20 ÷ 0.25 = 80 V