Problem solving tips

## Current Electricity

- Want to score better marks in exams? Have a look at some problem solving tips.
1
Tip 1:
Voltage division in a series circuit:
• First of all, find the equivalent (total) resistance of the circuit by simply adding up all the series resistors.
• Now the current drawn can be obtained by using the net resistance and the supply voltage.
• Now as the current remains constant for all the resistors, the voltage across any resistance can be obtained using Ohm's law.
Considering a shortcut, the voltage across any particular resistance can be obtained by using the formula:
Where is the voltage drop across particular resistance, is the resistance, and is the voltage of the source.
A power supply of electromotive force (e.m.f) and negligible internal resistance connected in series with resistors of resistance and as shown
A voltmeter measures the potential difference (p.d) across the  resistor and an ammeter measures the current in the circuit.
What are suitable ranges for the ammeter and for the voltmeter?
A
ammeter range voltmeter range
B
ammeter range voltmeter range
C
ammeter range voltmeter range
D
ammeter range voltmeter range
2
Tip 2:
Solving numerical based on Kirchhoff's Voltage Law:
• For all independent loops, consider a loop current in the loop in a clockwise (or counter-clockwise) direction. These loop currents will be the unknown variables that we need to determine.
• Apply KVL around each of the loops in the same clockwise direction to obtain the respective loop equations. While calculating the voltage drop across each resistor shared by two loops, both loop currents (in opposite positions) should be considered.
• Solve all the equations obtained for the loops and determine the unknown currents.
In the circuit shown, the current in the resistor is:

A
, from to
B
C
, from to
D
, from to
3
Tip 3:
Solve the parallel combination of equal resistances.
In the parallel combination of equal resistances, the net resistance is obtained as:
When are same, then the equation gets reduced as follow:
For equal resistors in parallel, equivalent resistance is:
A wire of uniform thickness with a resistance of  is cut into three equal pieces and they are joined in parallel. The equivalent resistance of the parallel combination will be :
A
B
C
D