Don't understand question 7.

Status
Not open for further replies.
zappy

zappy

Senior Member
Location
CA.
Question 6. The equivalent resistance of the 3 heater coils connected as shown is: Answer 5 ohms.

Question 7. If ammeter 2 reads 6 amps, ammeter 1 will read: Answer 18 amps.

I don't understand how they got this answer. Could someone explain this please. Thank you for your help.
 

Attachments

  • ELECTRICAL PROBLEM.jpg
    ELECTRICAL PROBLEM.jpg
    141.2 KB · Views: 0
The current through #1 is split three ways between the three 15 ohm resistors, #2 measures the current through one of the three.
 
It is a current divider. Ammeter #2 reads current through the top element. The parallel elements have the same resistance so what goes through the top element will equal what goes through the other two. Since we have resistances, the currents add to 6 amps at Y. In a closed loop, the current at Y equals the current at X. the current at X is the same as the current through the ammeter #1 or 6 amps.
 
zappy said:
Question 6. The equivalent resistance of the 3 heater coils connected as shown is: Answer 5 ohms.

Question 7. If ammeter 2 reads 6 amps, ammeter 1 will read: Answer 18 amps.

I don't understand how they got this answer. Could someone explain this please. Thank you for your help.
Click to expand...

Each resistor is pulling the same amount of current. Ammeter 2 measures only the current through one of the three resistors, so ammeter 1 which measures the total current will register three times that. It does not matter for this question what the resistances are, just that they are equal.

PS: 3 x 6 = 18. Show your work. :)

PPS: Extra credit question. If switch #1 is closed, does it short out only one of the three resistors or all of them? And what will ammeter #1 and ammeter #2 read then?
 
Last edited:
The book says each heater coil is pulling 2 amps.

The book says each heater coil is pulling 2 amps.

Plus what about the 20 ohm resistor. That must add to the total amps on ammeter 1.
 
zappy said:
Plus what about the 20 ohm resistor. That must add to the total amps on ammeter 1.
Click to expand...

A resistor does not "add amps". It causes a voltage drop based on the number of amps flowing through it. The amp value flowing through the 20 ohm resistor is exactly equal to the total of the amps through the three 10 ohm resistors. This is a characteristic of series circuits.

If, instead of being given the amps for meter #2 you had been given the applied voltage, then you would have to consider the 20 ohm resistor when calculating the current. (The voltage drop across all resistors in series would have to equal the applied voltage, therefore you can solve for the current.)
 
Status
Not open for further replies.
Top