Question

An electric bus operates by drawing direct current from two parallel overhead cables, at a potential difference of 600 V, and spaced 55 cm apart. When the power input to the bus’s motor is at its maximum power of 65 hp, (a) what current does it draw and (b) what is the attractive force per unit length between the cables?

Answer 1

An electric bus runs by drawing current from 2 parallel cable wires having a certain potential difference separated by certain distance. Calculate current drawn by the bus from relation of power of motor and current.

(a)

The relation between power, current and the potential difference is,

Here is the electric power, is the potential difference between cable wires and is the current drawn from the cable wires.

Suppose the motor of given power draws the current from the wires, then the current drawn is,

Convert power from horse power to watt,

Substitute, for V and in current equation,

The current drawn by 65 hp motor is .

(b)

The attractive force between two parallel wires is,

Here is Magnetic constant, and are the currents flowing through the wire and is distance between two wires.

Therefore force per unit length is,

Convert distance between wires from centimeter to meter,

Substitute, for, for and in force equation,

.

The attractive force per unit length in cable wires is.