Transformers and Electromagnetism

In summary, to operate an electric doorbell from a 120V 60Hz ac supply, a 1:10 transformer ratio is required and it must be connected as a step-down transformer. If the transformer is connected backwards, it will act as a step-up transformer with a ratio of 10:1 and supply a dangerously high voltage of 1200V to the doorbell, potentially causing damage. It is important to never reverse a power transformer, even without attaching the doorbell, as it can lead to damage or burning out of various components.
  • #1
mortymoose

Homework Statement


An electric doorbell requires a 12 V 60Hz ac supply
a)What turn ratio is required on a transformer to operate from a 120V 60Hz ac supply?
b)Step-up or step-down?
c)If the transformer is connected the wrong way around the circuit what voltage is supplied to the doorbell?

Homework Equations


Ns/Np =Vs/Vp
Vs>Vp ---stepup
Vs<Vp ---- step down

The Attempt at a Solution


a) so for this I have the Vs=12V and the Vp=120V... 12V/120V= 0.1 giving a 1:10 ratio
120V is too high for the 12V doorbell so it would need to be connected as a step down and convert its high voltage to a low voltage
b) then that makes this a step-down transformer because Vp is greater than Vs
c) This is the part that confused me a little.. So if it was connected backwards would that turn it into a step-up transformer changing the ratio to 10:1
Vs/Vp=Ns/Np
120V/12V=10turns/1turn
Vs=Vp*(Ns/Np)
Vs=120V(10/1)
Vs=1200V
and then 120*10=1200V supplied to the doorbell? And that would be way to much voltage for the doorbell to handle and damage it?
 
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  • #2
mortymoose said:
120*10=1200V supplied to the doorbell?
Yes, and that would burn the doorbell.
 
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  • #3
cnh1995 said:
Yes, and that would burn the doorbell.
Okay thank you!
 
  • #4
But don't try reversing a power transformer, even without attaching the doorbell.
The low voltage winding will have far too few turns, the core will saturate and large primary current will flow until (very quickly) something burns out (supply fuse or primary winding or connecting wires.)
 
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1. What are transformers and how do they work?

Transformers are devices that use electromagnetic induction to transfer electrical energy from one circuit to another. They consist of two or more coils of wire, known as the primary and secondary windings, which are wound around a common iron core. Alternating current flowing through the primary winding creates a changing magnetic field, which induces a voltage in the secondary winding. This voltage can then be used to power a separate circuit, with the number of windings on each coil determining the ratio of input to output voltage.

2. What is the role of electromagnetism in transformers?

Electromagnetism is the fundamental principle behind the operation of transformers. As mentioned, the alternating current in the primary coil creates a changing magnetic field, which in turn induces an alternating voltage in the secondary coil. This phenomenon is known as electromagnetic induction and is the basis for how transformers are able to transfer electrical energy from one circuit to another.

3. How do transformers impact the distribution of electricity?

Transformers play a crucial role in the distribution of electricity. They allow for the efficient transmission of power over long distances by stepping up the voltage at the power plant, reducing the current and thus minimizing energy loss during transmission. At the destination, transformers then step down the voltage to a level that is safe for use in homes and businesses.

4. Can transformers be used for anything other than electricity distribution?

While transformers are most commonly associated with electricity distribution, they can also be used for other purposes. For example, transformers are commonly used in electronic devices, such as audio amplifiers and power adapters, to step up or step down voltage as needed. They are also used in some medical equipment, such as magnetic resonance imaging (MRI) machines, to create strong magnetic fields.

5. What are some potential risks associated with transformers?

One potential risk associated with transformers is the release of electromagnetic radiation, which can interfere with other electronic devices. This is why transformers are often shielded and kept at a safe distance from other equipment. Another risk is electrical shock, as transformers can carry high voltages. It is important for trained professionals to handle and maintain transformers to prevent accidents or malfunctions.

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