Carbon-zinc dry cells (sometimes referred to as nonalkaline cells) have an emf of 1.54 V, and they are produced as single cells or in various combinations to form other voltages. (a) How many 1.54-V cells are needed to make the common 9-V battery used in many small electronic devices

We will need about Six (6) 1.54 Volts cells to make up the 9 Volts battery

Explanation:

A battery is simply the combination of two or more simple cells.

To achieve a higher voltage batteries, the non alkaline cells have to be connected in series.

hence we have

One cell = 1.54 volts

Two cells = 1.54 + 1.54 = 3.08 volts

Three cells = 1.54 + 1.54 + 1.54 = 4.62 Volts

Four cells = 1.54 + 1.54 + 1.54 + 1.54 = 6.16 Volts

Five cells = 1.54 + 1.54 + 1.54 + 1.54 + 1.54 = 7.7 Volts

Six cells = 1.54 + 1.54 + 1.54 + 1.54 + 1.54 + 1.54 = 9.24 Volts

Hence would will need a total of 6 cells to make 9 volts

6 cells are necessary.

Explanation:

a) The total emf when the cells are connected in series is equal to:

Vt = n*V

Where

n = number of cells = ?

V = emf of a single cell = 1.54 V

Replacing and clearing n:

n = Vt/V = 9/1.54 = 5.84 = 6