Sign in to follow this  
Followers 0

finding the power


5 posts in this topic

Posted

A.The battery has 7.5 V output voltage and 19 Ohm internal resistance. The battery is used to boot a small electric motor with 155 Ohm resistance. Find the power delivered to the motor.

so my first attempt was 7.5/19 =.394737A

then .394737^2*155 = 24.1517W

that was wrong so i I'm thinking this but I have only one try left:

7.5/(19+155) = .043103A

.043103^2*155 = .287976W

B.Two batteries with 2.8 voltage and 9.5 Ohm internal resistance each are connected in series. This battery pack is used to boot a small electric motor with 270 Ohm resistance. Find the power delivered to the motor.

This second question i did the same as the first but only adding the voltage = 2.8 +2.8 = 5.6 and adding the internal resistance R = 19

the 5.6/19 = .294737

.294737^2*270 = 23.4548W

And I also have only one try left with this guess:

5.6/(19+270) = .019377

.01937^2*270 = .101378W

Share this post


Link to post
Share on other sites

Posted

[ 7.5V/(19+155) ]^2 * 155 is right for A. Alternatively you could have used a voltage divider, but this works the same way in simple logic.

For B, [ (2.8+2.8)/(9.5+9.5+270) ]^2 * 270 is right. Too lazy to work out the math. Again, you could have used a voltage divider, but using I^2 R also works.

(Man, I miss doing basic circuits.)

Share this post


Link to post
Share on other sites

Posted

Thanks.

I'm having trouble with this one too:

eval_button.png

The battery is made by connecting 6 unit cells in series and then by connecting 8 of these series cells in parallel. Each unit cell has the voltage of 1.25 V and the internal resistance if 2.2 Ohm. What is the maximum power that can be delivered to the load by this battery?

My first try is this:

V(series) = 6*V

R(series) = 6*R

R(total) = 1/[8/(6R)]

so then P = V^2/R(total) = 48*V^2*R = 165W

Share this post


Link to post
Share on other sites

Posted

(Man, I miss doing basic circuits.)

Looking at this brings back painful memories of higher level electrical classes. :cry:

Share this post


Link to post
Share on other sites

Posted

Man, I love electrostatics, current electricity, and magnetism!

BTW, OP I have replied to the new thread you created for the second question.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0

  • Recently Browsing   0 members

    No registered users viewing this page.