Induced voltages and step-up transformers


by kitkat2950
Tags: induced, stepup, transformers, voltages
kitkat2950
kitkat2950 is offline
#1
Jul21-08, 02:28 PM
P: 7
I have been trying, but I still have 3 problems I can't get.

1)A simple generator has a 600 loop square coil 18.0 cm. on a side. How fast (in rev/s.) must it turn in a 0.730 T. field to produce a 120-V. peak output?

I think I need to use the equation Emax=NBAw. N=600 B=.730 A=.0324 Emax=120
I found w to be 8.456 but I didn't know if it was in rev/min or rev/s. So I tried that answer and then tried dividing it by 60 for seconds, but neither answer worked. Any help?



2)A step-up transformer increases 50 V. to 110 V. What is the current in amperes in the secondary as compared to the primary? Assume 100 percent efficiency.

I know the primary voltage is 50V and the secondary voltage is 110V. And I think Vp/Vs=Ip/Is, but I'm not sure how to find the answer w/o one of the currents.



3)A transformer has 32 turns in the primary and 181 turns in the secondary. Assuming 100 percent efficiency, by what factor does it change the voltage?

I think this one is basically the same as number 2, and I just don't understand what I am supposed to do. I think I'm supposed to divide one by the other, but when i put those answers in, they're not right.
Phys.Org News Partner Science news on Phys.org
Cougars' diverse diet helped them survive the Pleistocene mass extinction
Cyber risks can cause disruption on scale of 2008 crisis, study says
Mantis shrimp stronger than airplanes
alphysicist
alphysicist is offline
#2
Jul21-08, 03:13 PM
HW Helper
P: 2,250
Hi kitkat2950,

Quote Quote by kitkat2950 View Post
I have been trying, but I still have 3 problems I can't get.

1)A simple generator has a 600 loop square coil 18.0 cm. on a side. How fast (in rev/s.) must it turn in a 0.730 T. field to produce a 120-V. peak output?

I think I need to use the equation Emax=NBAw. N=600 B=.730 A=.0324 Emax=120
I found w to be 8.456 but I didn't know if it was in rev/min or rev/s. So I tried that answer and then tried dividing it by 60 for seconds, but neither answer worked. Any help?
The [itex]\omega[/itex] is angular frequency, which is not in rev/min or rev/s; what are the units of angular frequency?

Once you find [itex]\omega[/itex], you'll have to convert it to rev/s.




2)A step-up transformer increases 50 V. to 110 V. What is the current in amperes in the secondary as compared to the primary? Assume 100 percent efficiency.

I know the primary voltage is 50V and the secondary voltage is 110V. And I think Vp/Vs=Ip/Is, but I'm not sure how to find the answer w/o one of the currents.
It's strange that the ask for the current in the secondary in amperes. When they say "as compared to the primary" that suggests that what they are looking for is the ratio of the currrents. Was there a diagram or anything else in the problem?

Your equation is not correct. If the transformer is 100% efficient, what is not lost by the transformer?




3)A transformer has 32 turns in the primary and 181 turns in the secondary. Assuming 100 percent efficiency, by what factor does it change the voltage?

I think this one is basically the same as number 2, and I just don't understand what I am supposed to do. I think I'm supposed to divide one by the other, but when i put those answers in, they're not right.
What is the relationship between voltage and turns in a transformer? (Without knowing what numbers you used and got, it's difficult to determine what you might have done wrong.)
annythewitch
annythewitch is offline
#3
Nov7-08, 08:47 PM
P: 2
2. the ratio you want is:

Vs/Vv=Ns/Np: Is/Ip=Np/Ns >>> Vs/Vp=Ip/Is >>> Is/Ip=Vp/Vs = 50/100= .5

alphysicist
alphysicist is offline
#4
Nov7-08, 11:36 PM
HW Helper
P: 2,250

Induced voltages and step-up transformers


Quote Quote by annythewitch View Post
2. the ratio you want is:

Vs/Vv=Ns/Np: Is/Ip=Np/Ns >>> Vs/Vp=Ip/Is >>> Is/Ip=Vp/Vs = 50/100= .5
No, I don't believe that's the answer. You seem to have put in a wrong number.

Also, you have put in a few extra steps. There is 100% efficiency, so the power is the same on both sides, so you can immediately write down:

[tex]
I_p V_p = I_s V_s
[/tex]

and get the ratio in the next step.
annythewitch
annythewitch is offline
#5
Nov8-08, 12:09 AM
P: 2
you are right. I mistyped the fraction. it should have been 50/110, and yeah, your way is easier.


Register to reply

Related Discussions
Step down transformers & efficiency?! General Physics 11
Step up and step down transformers Introductory Physics Homework 6
How can you get power used from step down transformers Introductory Physics Homework 2
Induced Voltages and Inductance Introductory Physics Homework 2