Course

AS Physics: Electricity and the Atom (9702)

Name: AS Physics: Electricity and the Atom (9702)
Price: 1999 BDT

9702 topics 9, 10 and 11. Current as counted carriers, then circuits, then what the carrier is made of: the quark model as an answer, not a table to memorise.

44 lessons4h 38mEnglish

What you'll learn

Explain current as a flow of counted carriers, and use that to make drift velocity obvious
Distinguish resistance from resistivity, and say which one belongs to the material
Apply Kirchhoff’s two laws, and recognise which one a given junction or loop needs
Work with e.m.f. and internal resistance, including why a terminal reading drops under load
Use the quark model to account for charge in a beta decay, rather than quoting the products

Requirements

AS topic 5: work, energy and power, since potential difference is energy per unit charge
AS topic 1: units and prefixes, and the ability to check an equation for homogeneity
Able to rearrange an equation with several symbols in it
O Level Physics circuit symbols and the idea of a complete circuit

Course content

44 lessons · 4h 38m

9.1-9.3 · Electricity

Current as the rate of flow of charge, why the electrons drift so slowly, the volt as a joule per coulomb, resistance and Ohm’s law, the I-V graphs of a wire, a lamp and a diode, resistivity and the effect of temperature.

0/12

Current is charge per second

Your charger is marked 2 A. Find out what was already moving inside the copper.

Preview6m 2.

Why the electrons crawl: I = Anvq

The lamp lights at once, yet the drift velocity is under a millimetre per second.

Preview7m

One volt is one joule per coulomb

Move a charge between two points and read the energy it gives up on the way.

Resistance is a ratio you measure

Double the e.m.f. across a lamp and predict what happens to the ratio V over I.

Ohm’s law is a claim, not a definition

A metal wire at constant temperature gives a straight line through the origin.

The filament lamp bends its graph

The filament reaches 2500 degrees Celsius, and its resistance does not stay put.

The diode conducts one way only

Almost nothing below the 0.6 V knee, then a steep rise. Reverse it and predict.

Heat a metal, heat a semiconductor

One resistance rises with temperature and the other falls. Predict which is which.

Resistivity belongs to the material

Twice the length, twice the resistance. Then R = rho L over A, and why thin cable warms.

10.

Electrical power: P = VI

Halve the lamp resistance on a fixed supply, then predict what the power does.

11.

One exam question, end to end

Eleven marks, five parts, no options: resistance, current, power, drift velocity, then why the lamp is instant.

12.

Electricity: quick revision

Reconnect charge flow, resistance and power through one physical circuit story.

10.1-10.3 · D.C. circuits

Electromotive force and what a cell keeps for itself, terminal potential difference, Kirchhoff’s two laws and the series and parallel rules that follow from them, the potential divider, a sensing divider and the potentiometer.

0/16

Electromotive force is energy per coulomb

A cell is not a store of current. Find out what it actually supplies to each coulomb.

Preview6m 2.

Kirchhoff’s first law: charge is never stored at a junction

Two branches, two different currents. Predict the reading before the junction.

Preview6m

Kirchhoff’s second law: the loop adds up

Three components in one loop. Predict the third potential difference from the other two.

Resistors in series add

The same current everywhere, and the potential differences share out in ratio.

Parallel gives less than the smallest

Two 200 Ω resistors side by side. Predict the total before you switch to parallel.

A cell keeps some of its own e.m.f.

The tube light dims when the fridge starts. The reason is inside the supply.

Terminal p.d. = E − Ir

Halve the load resistance, double the current, and predict the lost volts.

Two resistors split the voltage

Predict the 6 V output from a 9 V supply before you read the divider.

A divider that senses temperature

Warm the thermistor and predict which way the output potential difference moves.

10.

The potentiometer draws no current at balance

Potential grows evenly along a uniform wire, so a balance length measures e.m.f.

11.

Complex to simple: reducing a network before you solve it

Four resistors, none obviously in series or parallel. Fold the far node away and the pair you could not see appears.

12.

Solving a circuit the series and parallel rules cannot touch

Two cells pushing against each other. Three unknown currents, three equations, and one of the answers comes out negative.

13.

What an ammeter and a voltmeter are actually made of

One galvanometer, one resistor. Where that resistor goes decides which instrument you are holding, and why each has the resistance it does.

14.

Arranging cells: more in series is not always more current

Twenty-four cells and one resistor. Every cell added in series brings its own internal resistance, and past a point that costs more than it gains.

15.

One exam question, end to end

Nine marks, four parts, no options: a parallel load, the current, the terminal p.d., then the power wasted inside.

16.

D.C. circuits: quick revision

Reconnect junctions, loops and real cells, then rehearse a reliable circuit-solving route.

11.1-11.2 · Particle physics

What the alpha-scattering experiment proved about the atom, how a nuclide is written and counted, the four decay routes and the equations that must balance, and the quarks that make a proton a proton.

0/13

What alpha scattering proved

One alpha particle in 8000 came back. Work out what inside the foil could do that.

Preview6m 2.

How small the nucleus is

A 5.0 MeV alpha particle stops somewhere. Use W = qΔV to find where.

Preview7m

Proton number and nucleon number

Two counts fix a nuclide, and the notation puts both of them on the symbol.

Isotopes: same element, different nucleus

Uranium-235 and uranium-238 behave the same chemically and very differently in a reactor.

Alpha decay and the balanced equation

The smoke alarm on the ceiling holds an alpha emitter. Balance its decay equation.

Beta-minus decay

The nucleus holds no electrons, yet it emits one. Find where that electron comes from.

Why the neutrino had to exist

A two-body decay gives one fixed energy. Beta particles arrive with a range of energies.

Beta-plus decay

A positron bends the opposite way in the same field, so the charge must be opposite.

Gamma emission changes no numbers

The nucleus loses energy without losing a nucleon, and the photon goes a long way.

10.

The quarks inside a proton

Fill three slots with up and down quarks and see which combinations give +1 and 0.

11.

Beta decay is one quark changing

Change one down quark to an up quark and the neutron becomes a proton.

12.

One exam question, end to end

Seven marks, five parts, no options: four nuclide numbers to balance, then a quark change to explain.

13.

Particle physics: quick revision

Reconnect nucleus notation, decay equations and quark structure, then repair a conservation mistake.

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