Circuit Resistance: Find Total Resisitance with Cells Connected in Series

[aurao2003]

Homework Statement

hi
i am wondering if this is correct. this is the question;
Three cells, each of e.m.f. 1·5 V and internal resistance 0·50 Ω, are connected in series to
make a battery of e.m.f. 4·5V. The battery is connected to a resistor, R, of resistance 6·0 Ω.

Homework Equations

V= i/R

The Attempt at a Solution

TOTAL VOLTAGE = 4.5V
TOTAL RESISTANCE = 6.5 OHMS
but the answer states the total resistnace is 7.5 ohms.
can someone kindly explain how?
thanks

 

[Fightfish]

Three cells, each of e.m.f. 1·5 V and internal resistance 0·50 Ω, are connected in series to
make a battery of e.m.f. 4·5V. The battery is connected to a resistor, R, of resistance 6·0 Ω.

Three cells of 0.50Ω + a resistor of 6·0 Ω = ?

 

[aurao2003]

Three cells of 0.50Ω + a resistor of 6·0 Ω = ?

silly me.
total internal resistance = 1.5 ohms (3x0.5 ohms)
total resistance = 1.5 +6= 7.5 ohms

thanks a million

 

[soothsayer]

EACH of the three cells has internal resistance of 0.5Ω

0.5Ω + 0.5Ω + 0.5Ω = 1.5Ω

add that to the resistor of 6Ω connected to the battery and you get 7.5Ω! =)

You probably thought the three resistors had 0.5Ω in total, easy mistake to make in reading the problem.

EDIT: nevermind, seems you got it already.

 

[aurao2003]

EACH of the three cells has internal resistance of 0.5Ω

0.5Ω + 0.5Ω + 0.5Ω = 1.5Ω

add that to the resistor of 6Ω connected to the battery and you get 7.5Ω! =)

You probably thought the three resistors had 0.5Ω in total, easy mistake to make in reading the problem.

EDIT: nevermind, seems you got it already.

yeah. not good for a budding engineer. thanks