18.5 CHAPTER 18. ELECTROMAGNETISM
Transformer technologyhas made long-range electric power distributionpractical. Without the ability
to efficiently step voltage up and down, it wouldbe cost-prohibitive to construct power systems for
anything but close-range(within a few kilometres) use.
As useful as transformers are, they only work with AC, not DC. This is because the phenomenonof
mutual inductance relies on changing magnetic fields, and direct current (DC) can only produce
steady magnetic fields, transformers simply willnot work with direct current.
Of course, direct current may be interrupted (pulsed) through the primary winding of a transformer to
create a changing magnetic field (as is done in automotive ignition systems to produce high-voltage
spark plug power from alow-voltage DC battery), but pulsed DC is not that different from AC.
Perhaps more than any other reason, this is whyAC finds such widespread application in power
systems. See simulation: VPlxa at http://www.everythingscience.co.za)Real-world applications ESBIB
Transformers are very important in the supply ofelectricity nationally. Inorder to reduce energy
losses due to heating, electrical energy is transported from power stations along power lines at high
voltage and low current. Transformers are usedto step the voltage up from the power station to the
power lines, and step itdown from the power lines to buildings where it is needed.Exercise 18 - 3
- Draw a sketch of themain features of a transformer
- Use Faraday’s Law toexplain how a transformer works in words and pictures.
- Use the equation forFaraday’s Law to derivean expression involvingthe ratios of the voltages
and the number of windings in the primary andsecondary coils. - If we have Np= 100 and Ns= 50, and we connect the primary winding to a230 V, 50Hz
supply, then calculate the voltage on the secondary winding. - State the difference between a step-up and astep-down transformer in both structure and
function. - Give an example of the use of transformers.
More practice video solutions or help at http://www.everythingscience.co.za(1.) 01hf (2.) 01hg (3.) 01hh (4.) 01hi (5.) 01hj (6.) 01hk18.5 Motion of a charged particle in a magneticfield
ESBIC
When a charged particlemoves through a magnetic field it experiences aforce. For a particle thatis
moving at right angles tothe magnetic field, the force is given by:F = qvB