Transcript Transformers

13.5 Transformers
Different electrical devices require different amounts of
electrical energy to operate. An electric stove requires a
lot of electrical energy while a lamp requires very little.
Some devices require different voltages and currents. A
computer may require 12 V to operate, so the voltage in
your home must be lowered from 120 V to 12 V.
Transformers are electromagnetic devices that are used
to lower or raise the AC voltage to the value that any
electronic device is designed for.
Adapters such as cellphone and laptop chargers have
transformers as part of their internal circuitry.
13.5 Transformers
To understand how a transformer works, recall Faraday’s Ring from Section 13.1.
The ring has a primary and a secondary circuit that are not in direct physical
contact, however the current in the primary circuit induces a current in the
secondary circuit.
A changing magnetic field is required for electromagnetic induction, which can be
produced using alternating current. AC in the primary coil is the most critical part
of producing AC in the secondary coil of Faraday’s Ring.
13.5 Transformers
Transformers have a different number of windings on the primary circuit compared
to the secondary circuit.
A step-down transformer has fewer windings on the secondary circuit than the
primary circuit; Voltage on the secondary side is less than voltage on the primary
side.
A step-up transformer has more windings on the secondary circuit than the
primary circuit; Voltage on the secondary side is higher than voltage on the
primary side.
13.5 Conservation of Energy in Transformers
According to the law of conservation of energy, energy going into the primary coil
must equal energy coming out of the secondary coil.
Power in an electrical circuit can be expressed as a product of voltage and current,
or P = VI; A change in energy can be expressed as ∆E = P∆t.
For primary and secondary sides of the transformer:
13.5 Transformer Equations
By grouping current (I) and voltage (V):
Voltage (V) in the coil is directly proportional
to the number of windings (N):
Current (I) is inversely proportional to
the number of windings (N):
Combining all ratios into one equation:
SP #1 p.607
SP #1 p.608
13.5 Homework
Practice # 1, 2 p.608 – Tutorial 1
Practice # 1, 2 p.608 – Tutorial 2
Questions # 1, 5, 7-9 p.609