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  • Explain how a transformer works.
  • Calculate voltage, current, and/or number of turns given the other quantities.

Transformers do what their name implies—they transform voltages from one value to another (The term voltage is used rather than emf, because transformers have internal resistance). For example, many cell phones, laptops, video games, and power tools and small appliances have a transformer built into their plug-in unit (like that in [link] ) that changes 120 V or 240 V AC into whatever voltage the device uses. Transformers are also used at several points in the power distribution systems, such as illustrated in [link] . Power is sent long distances at high voltages, because less current is required for a given amount of power, and this means less line loss, as was discussed previously. But high voltages pose greater hazards, so that transformers are employed to produce lower voltage at the user’s location.

A photo graph of two plug in transformers operated on voltages other than common one hundred twenty volt AC.
The plug-in transformer has become increasingly familiar with the proliferation of electronic devices that operate on voltages other than common 120 V AC. Most are in the 3 to 12 V range. (credit: Shop Xtreme)
The figure shows a transmission power system. It shows the various stages in a power transmission system from the power plant to the house hold with the help of images. The first image is of a power plant. The voltage generated is at twelve volts. This voltage is shown to pass on to a step up transformer through cables. From the step up transformer the current passes through a high voltage transmission line at four hundred kilo volt. The high voltage transmission line is shown passing on three towers. The current is then passed to a step down transformer substation. The current is step down to twelve volts. This is now passed through power transmission lines on poles. This current reaches a step down transformer which is fixed on a pole. Here the voltage is further stepped down to two hundred forty volts. Current is then supplied to an individual household at two hundred forty volts.
Transformers change voltages at several points in a power distribution system. Electric power is usually generated at greater than 10 kV, and transmitted long distances at voltages over 200 kV—sometimes as great as 700 kV—to limit energy losses. Local power distribution to neighborhoods or industries goes through a substation and is sent short distances at voltages ranging from 5 to 13 kV. This is reduced to 120, 240, or 480 V for safety at the individual user site.

The type of transformer considered in this text—see [link] —is based on Faraday’s law of induction and is very similar in construction to the apparatus Faraday used to demonstrate magnetic fields could cause currents. The two coils are called the primary and secondary coils . In normal use, the input voltage is placed on the primary, and the secondary produces the transformed output voltage. Not only does the iron core trap the magnetic field created by the primary coil, its magnetization increases the field strength. Since the input voltage is AC, a time-varying magnetic flux is sent to the secondary, inducing its AC output voltage.

The figure shows a simple transformer with two coils wound on either sides of a laminated ferromagnetic core. The set of coil on left side of the core is marked as the primary and there number is given as N p. The voltage across the primary is given by V p. The set of coil on right side of the core is marked as the secondary and there number is represented as N s. The voltage across the secondary is given by V s. A symbol of the transformer is also shown below the diagram. It consists of two inductor coils separated by two equal parallel lines representing the core.
A typical construction of a simple transformer has two coils wound on a ferromagnetic core that is laminated to minimize eddy currents. The magnetic field created by the primary is mostly confined to and increased by the core, which transmits it to the secondary coil. Any change in current in the primary induces a current in the secondary.

For the simple transformer shown in [link] , the output voltage V s size 12{V rSub { size 8{s} } } {} depends almost entirely on the input voltage V p size 12{V rSub { size 8{p} } } {} and the ratio of the number of loops in the primary and secondary coils. Faraday’s law of induction for the secondary coil gives its induced output voltage V s size 12{V rSub { size 8{s} } } {} to be

V s = N s Δ Φ Δ t , size 12{V rSub { size 8{s} } = - N rSub { size 8{s} } { {ΔΦ} over {Δt} } } {}

where N s size 12{N rSub { size 8{s} } } {} is the number of loops in the secondary coil and Δ Φ size 12{ΔΦ} {} / Δ t size 12{Δt} {} is the rate of change of magnetic flux. Note that the output voltage equals the induced emf ( V s = emf s size 12{V rSub { size 8{s} } ="emf" rSub { size 8{s} } } {} ), provided coil resistance is small (a reasonable assumption for transformers). The cross-sectional area of the coils is the same on either side, as is the magnetic field strength, and so Δ Φ / Δ t size 12{ΔΦ} {} is the same on either side. The input primary voltage V p size 12{V rSub { size 8{p} } } {} is also related to changing flux by

Questions & Answers

What is half-life
Godwin Reply
what is fluid
Anthony Reply
anything that flows is Liquid.
a substance that has no specific shape
How submarines floats one water the same time sink in water
Courage Reply
A submarine has the ability to float and sink. The ability to control buoyancy comes from the submarine'strim or ballast tanks which can be filled with either water or air, depending on whether the submarine needs to floator sink. When the submarine floats it means its trim tanks are filled with air
define electromagnetic radiation
what is work
Ojo Reply
Force times distance
product of force and distance...
Is physics a natural science?
Adebisi Reply
what is the difference between a jet engine and a rocket engine.
Samuel Reply
explain the relationship between momentum and force
Joseph Reply
A moment is equivalent multiplied by the length passing through the point of reaction and that is perpendicular to the force
How to find Squirrel frontal area from it's surface area?
Pooja Reply
how do we arrange the electronic configuration of elements
Muhammed Reply
hi guys i am an elementary student
benedict Reply
are you an elementary student too?
no bro
what is the four equation of motion
what is strain?
Change in dimension per unit dimension is called strain. Ex - Change in length per unit length l/L.
strain is the ratio of extension to length..=e/l...it has no unit because both are in meters and they cancel each other
How is it possible for one to drink a cold drink from a straw?
Karanja Reply
most possible as it is for you to drink your wine from your straw
state the law of conservation of energy
Sushma Reply
energy can neither be destroy or created,but can be change from one form to another
it can neither be created nor destroyed
its so sample question dude
what is the difference between a principle and a law?
Mary Reply
where are from you wendy .?
you are beautiful
are you physics student
laws are ment to be broken
hehe ghulam where r u from?
principle are meant to be followed
south Africa
here Nigeria
principle is a rule or law of nature, or the basic idea on how the laws of nature are applied.
Rules are meant to be broken while principals to be followed
principle is a rule or law of nature, or the basic idea on how the laws of nature are applied.
what is momentum?
prakash Reply
is the mass times velocity of an object
it is the product of mass and velocity of an object.
The momentum possessed by a body is generally defined as the product of its mass and velocity m×v
momentum is the product of the mass of a body of its velocity
what about kg it is changing or not
vijay Reply
no mass is the quantity or amount of body so it remains constant everywhere
remains constant
mass of an object is always constant. and that is universally applied.
mass of a body never changes but the weight can change due to variance of gravity at different points of the world
what is hookes law
mass of an object does not change
Practice Key Terms 4

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