Electricity
Was browsing through my tuition notes folder and felt like sharing some physics notes.
I have read a lot of guidebooks with detail notes. In fact, there are a lot of pretty good ones. However, it takes a disciplined child to read them thoroughly and digest them.
Also, one of my student asked me “Wah teacher, so many points even in the guidebook, how to memorise ALL?”
Most of my students do not fancy their textbook materials as there are a lot of details.
Teaching some students on electricity now. So i compiled a few key points on this topic.
· V=IR (Main formula in this chapter)
· Identifying Series and parallel circuit
(If you do not know how to differentiate a series and parallel circuits, please PM me.)
Series Circuit
· Ammeter must always connected in series to show reading if not ZERO.
· Rtotal = R1+R2 (series)
· For series, everywhere you put the ammeter, current is the same ( NOT FOR PARALLEL).
Parallel Circuit
· 1/Rt = 1/R1+ 1/R2, It = I1+I2
· In parallel circuit, the more bulbs or resistors, R decrease, I increase.
Circuit symbols – Be familiar with these symbols
Resistance
· Nichrome has higher R than Cu.
More heating effect. I decreases, less bright if nichrome is used.
Resistance depends on
(a) length of conductor
(b) cross-sectional area of conductor
(c) temp of conductor
(d) type of conductor ( Please note that silver has better conductivity than copper and gold. But it is seldom used as conductors/wires because it oxidise easily. Although gold has a lower conductivity than copper, it is used extensively in semiconductor chips because its reactivity is very low.)
Short circuit
A short circuit is an abnormal connection between two nodes of an electric circuit intended to be at different voltages. (Wikipedia)
This results in an excessive current, causing overheating, circuit damage, fire and maybe explosion.
***A common type of short circuit occurs when the positive and negative terminals of a battery are connected with a low-resistance conductor, like a wire. ***
***Often comes out in tests and exams***
Calculating Electrical Power
Electrical power(W) = Energy converted (J)/Time (s)
Electrical energy used = electrical power (kW) * Time (hr)
Cost = Electrical energy used (kWh) * Electricity rate