Question

A light bulb of constant resistance R= 30.0 Ω is powered by two voltaic cells, each with voltage V = 1.55 V and energy content U= 3.90 Wh. The two cells can be connected either in series or in parallel.Foreach type of connection, find(a) thepower of the bulb,(b) the amount of time the bulb will remain lit.(c) Compare and contrast the advantages and disadvantages of the two types of connections. (a. 0.32W, 0.080W, b. 12.18 hours, 49.75 hours)

Answer 1

(a)

when connected in series, the output voltage doubles

so,

P = V² / R

P = (2 * 1.55)² / 30

P = 0.32 W

When connected in parallel, the output voltage remains same

P = 1.55² / 30

P = 0.08 W

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(b)

we know

P = E/t

t = E / P

so,

In series case

t = 3.90 / 0.32

t = 12.18 hours

in parallel case

t = 3.90 / 0.08

t = 48.75 hours

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(c)

When we connect two identical batteries ( or cells) in parallel, the output capacity is doubles while the output voltage is same.

If two identical batteries are connected in series, the output voltage is doubled but the output capacity is kept the same as either battery.