Introduction 

An electric circuit is an uninterrupted, conductive, complete, and closed path through which electrons flow from a source of electric power or source of energy through a device and returns to its source to complete the flow. 

On connecting the electric circuit to a battery, electrons flow from the battery’s negative terminal through one or more electrical devices like a bulb, for example, and then flow back to the positive terminal of the source of the power that is the battery in this case. Classification of these happens on the basis of the different ways in which circuits can be wired.

Combination of cells

When electrical devices are connected in a series one after another, it is called a combination of cells in a series, whereas in a combination of cells in a parallel circuit, the current makes its way through two or more paths.

Classification of circuits happens on the basis of the different ways in which circuits are wired.

• Combination of cells in series
• Combination of cells in parallel

Combination of cells in a series

In combination of cells in a series, the cells are connected in a series to each other like a loop. The negative terminal of the first cell is connected to the positive one of the second cell, and the negative terminal of the second cell is connected to the positive one of the third cell and so on, creating a series of cells that are connected end to end with each other, allowing a smooth flow of electrons from the positive terminal of the source to the device. The return journey of the electrons happens oppositely, and they return to the positive terminal of the source of energy. The starting point in the combination of cells in a series is the negative terminal, and the ending point on return is the positive terminal.

Hence, in the case of a combination of cells in a series, the EMF of the battery is connected to the sum of the EMF of the individual cells.

If the overall EMF of the battery is E;

the number of cells is n;

Then, the combination of overall EMF of the battery is:

E = E1 + E2 + E3 + E4 + ………..+ En

Similarly, if the overall resistance of the battery is R;

the number of cells is n;

Then, the combination of the overall resistance of the battery is:

R = R 1 + R 2 + R 3 + R 4 + ….+ R n

Advantages of a combination of cells in series

• The design of a combination of cells in a series is simple and easily understandable.
• Quick overheating does not occur.
• Its higher output voltage assists in the addition of more power appliances.
• The current that is carried throughout the circuit remains the same.

Disadvantages of a combination of cells in series

• An increase in the total number of components increases the circuit resistance.
• The occurrence of a fault at one point in the circuit will break the whole circuit.

Combination of cells in a parallel

In a combination of cells in parallel, the current is divided amongst various cells. In this type of combination of cells, all the positive terminals are connected to each other, and all the negative terminals are connected to each other, and the combination has a parallel structure that does not connect the positive and negative terminals of the cells like that of the combination cells in series. 

Suppose n cells of emf E are connected in a parallel combination. In parallel, combination emf has the same value so equivalent emf will be equal to E.

Now if the internal resistance of these cells are r1, r2, r3,……..rn, so the equivalent resistance of this combination will be

1/req = 1/r1 + 1/r2 + 1/r3 +………+ 1/rn.

Advantages of the combination of cells in parallel

• Damage to any one component in a combination of cells in a parallel circuit does not result in the stoppage of the, and its flow continues through the other components; this structure assists in the other components working efficiently in the event of damage to one of the components.
• As the voltage is the same across every component in a combination of cells in a parallel circuit, it improves efficiency.
• Connections or disconnections of new components are hassle-free in a combination of cells in a parallel circuit without adversely impacting the working of other components.

Disadvantages of a combination of cells in parallel

• An additional voltage source cannot be applied to a combination of cells in a parallel circuit. 
• It requires a lot of wiring.                                          

Conclusion

When electrical devices are connected in a series one after another, it is called a combination of cells in a series, whereas in a combination of cells in a parallel circuit, the current makes its way through two or more paths. In a combination of cells in series, the design of the cells is simple and easily understandable, does not result in quick overheating, the current remains the same throughout the circuit, and higher voltages assist in the addition of more power appliances. In a combination of cells in parallel, damage to any one component does not result in the stoppage of the circuit, and its flow continues through the other components. This assists in the efficiency of other components in the event of damage to one of the components.