Question

Seven equal resistance each of resistance 2 ohm are connected with a battery of 3v in a circuit . If i1 is the current when switch is open and i2 is the current when the switch is closed the ratio of i1/i2 is

Answer 1

Unlike current which flows around a closed electrical circuit in the form of electrical charge, potential difference does not move or flow it is applied.

The unit of potential difference generated between two points is called the Volt and is generally defined as being the potential difference dropped across a fixed resistance of one ohm with a current of one ampere flowing through it. In other words, one volt = one amp x one ohm, or V = IxR.

Ohm’s Law states that for a linear circuit the current flowing through it is proportional to the potential difference across it so the greater the potential difference across any two points the bigger will be the current flowing through it.

For example, if the voltage at one side of a 10Ω resistor measures 8Vand at the other side of the resistor it measures 5V, then the potential difference across the resistor would be 3V ( 8 – 5 ) causing a current of 0.3A to flow.

If however, the voltage on one side was increased from 8V to say 40V, the potential difference across the resistor would now be 40V – 5V = 35V causing a current of 3.5A to flow. The voltage at any point in a circuit is always measured with respect to a common point, generally 0V.

For electrical circuits, the earth or ground potential is usually taken to be at zero volts ( 0V ) and everything is referenced to that common point in a circuit. This is similar in theory to measuring height. We measure the height of hills in a similar way by saying that the sea level is at zero feet and then compare other points of the hill or mountain to that level.

In a very similar way we can call the common point in a circuit zero volts and give it the name of ground, zero volts or earth, then all other voltage points in the circuit are compared or referenced to that ground point. The use of a common ground or reference point in electrical schematic drawings allows the circuit to be drawn more simply as it is understood that all connections to this point have the same potential. For example: