NEB Class 11 • Physics • Focused Revision

Solids Study Guide: NEB 11 Physics

Make every band diagram explain a material property. Retrieve occupancy, gap, carrier and doping ideas separately before combining them in exam answers.

Seven-session band-theory plan
Diagram and carrier-accounting drills
Misconception repair and timed test

Band occupancy and energy gaps explain contrasting conductivity.

Revision boundary

Study the qualitative CDC scope with precise language

The CDC Physics curriculum specifies qualitative energy bands, comparison of metals, insulators and semiconductors, and intrinsic versus extrinsic semiconductors. Read the paired Solids concept guide first and use OpenStax band theory to verify the model.

Your evidence for mastery is not a coloured diagram alone. Each sketch must carry an energy axis, band names, occupancy or available states, gap size and one sentence connecting those features to mobile carriers. Revise the DC Circuits Study Guide if current, resistance and conventional direction are weak.

Knowledge map

Use four questions for every solid

Allowed states

Which energy bands exist and how are they separated?

Occupancy

Which states are filled and which nearby states are empty?

Carriers

Are electrons, holes or both mobile?

Control

How do purity, doping, light and temperature alter carriers?

Answering these questions prevents shallow definitions. A material conducts when charge carriers can respond into available states under an electric field. “It has free electrons” is incomplete if occupancy and accessible states are not described.

Seven sessions

A spaced plan with visible exit evidence

Session	Focus	Exit evidence
1	Atomic levels to bands	Three annotated sequence diagrams
2	Valence, conduction and forbidden gaps	12 label-and-explain cards
3	Metal, semiconductor, insulator	Nine classifications with reasons
4	Intrinsic carriers and holes	Six carrier-accounting explanations
5	Donor and acceptor doping	Eight n/p-type contrast items
6	Temperature, light and applications	Four claim–mechanism–limit paragraphs
7	Timed mixed test and repair	80% with no repeated carrier mistake

Start each session by redrawing the previous day’s key diagram from memory. Retest errors after two days using differently shaped diagrams, since energy structure—not familiar artwork—must drive the classification.

Diagram routine

Build a band diagram in six deliberate moves

Draw energy increasing upward.
Draw the valence band and show whether it is filled or partly filled.
Draw the conduction band or overlapping available states.
Mark the forbidden gap qualitatively.
Add electrons or holes only when the question introduces excitation or doping.
Write a sentence linking available states to conductivity.

Contrast pair

In an insulator sketch, show a filled valence band and a relatively large gap to empty conduction states. In an intrinsic semiconductor at room temperature, keep the smaller gap and show a few electrons promoted upward with equal holes left below. Do not fill the gap with carriers; it contains no allowed states in the simple model.

Practise reading diagrams backward: cover the material label and infer it from occupancy and gap. Then cover the gap and predict how the classification could change if the available states overlapped.

Carrier-accounting routine

Track pairs, donors, acceptors and neutrality

Intrinsic sample

Thermal excitation creates 6×10¹³ conduction electrons per cubic metre. The simple intrinsic model has the same hole concentration. If 1×10¹³ pairs recombine, both concentrations fall to 5×10¹³ m⁻³.

n-type sample

Donor impurities add easily excited electron states, so electrons dominate conduction. Holes still exist as minority carriers at nonzero temperature. The ionised donors are fixed positive lattice sites, balancing mobile negative charge.

p-type sample

Acceptor impurities make hole production easier, so holes dominate. Mobile minority electrons may still be present. The fixed acceptor ions balance the effective positive carrier charge.

Use the OpenStax doping explanation to check donor and acceptor language. Avoid the false shortcut “n means negative crystal, p means positive crystal.”

Explanation practice

Use claim, band evidence, carrier mechanism and limit

For “Why does silicon conductivity increase when heated?”, write: conductivity generally increases over the relevant range; thermal energy promotes more electrons across the small gap; this creates additional conduction electrons and holes; the simple statement omits detailed scattering, contacts and extreme-temperature effects.

For “Why does copper behave differently?”, write: a metal already has a partly filled or overlapping band with many carriers; heating mainly increases lattice vibration and scattering in the ordinary range; therefore its resistance usually increases. Do not explain both materials by carrier number alone.

For a sensor application, connect input to carrier change and then to measured circuit output. A photoconductor uses suitable photons to alter carrier population; a thermistor uses a temperature-dependent resistance. State that calibration, material choice and device construction are necessary.

Nepal-relevant electronics such as solar lamps, phone chargers and temperature controls use semiconductor devices, but a bulk semiconductor model is not a full circuit explanation. Detailed p–n junction behaviour belongs to a later unit.

Timed transfer test

A thirty-minute Solids paper

Explain how atomic levels become bands.
Define valence band, conduction band and forbidden gap.
Classify three unlabelled band diagrams with evidence.
Compare a metal, semiconductor and insulator.
Explain intrinsic electron–hole pair creation.
Distinguish donor and acceptor doping.
Name majority and minority carriers in n-type and p-type.
Correct “p-type material carries a net positive charge.”
Explain opposite temperature trends qualitatively.
Write a light-sensor paragraph with one model limitation.

Mark diagram, occupancy, gap, carrier, mechanism and limit separately. If the name is correct but the band evidence is missing, award only partial credit. After marking, redraw every failed classification with a changed gap or occupancy and explain the new result.

Create an error log with codes: axis, band label, occupancy, gap, hole, donor, acceptor, neutrality, temperature and application. Retest a failed code after 48 hours from an empty page, then one week later in a mixed set.

For online or physical NEB tuition, call 9846662070.

Frequently asked questions

Questions students ask while studying Solids

What should I revise first?

Revise energy, electric current and resistance, then learn to read a vertical energy-band diagram.

How do I distinguish a semiconductor from an insulator?

Both may have filled valence bands, but the semiconductor has a smaller gap and more readily generated carriers.

Are holes real particles?

A hole is an effective positive carrier describing an unoccupied valence state and collective electron motion.

Which dopant produces n-type material?

A donor with an extra valence electron relative to the host produces electron-majority n-type material.

Why is an extrinsic semiconductor neutral?

Mobile carrier charge is balanced by fixed ionised impurity atoms in the lattice.

Where can I get Solids revision help?

Call 9846662070 for current online or physical NEB tuition schedules and fees.

References and next steps

Sources and related study guides

Return to the concept guide after marking and continue into Recent Trends in Physics. Curriculum scope and time-sensitive institutional pages were checked on 2 August 2026; follow current CDC, NEB and school instructions if requirements change.

Transfer practice

Use unfamiliar evidence instead of memorised labels

A strong study guide must prepare you for a diagram or observation you have not seen before. When a question presents two bands, begin with occupancy and available states. Ask whether the highest occupied band is partly filled, overlaps another band, or is separated from the next allowed band. Only then name the material. This order prevents a common mistake: calling every visible gap an insulator without judging its relative size or the possibility of thermal excitation.

Try this reasoning drill without notes. Material A has a completely filled lower band and an empty upper band separated by a very large gap. Material B has a narrow gap and conductivity that increases strongly with temperature. Material C has a partly filled uppermost band. Predict the broad class of each material, identify the mobile carrier story, and write one sentence connecting the band picture to the observation. Check your answer against the OpenStax band-theory explanation, then rewrite any sentence that merely repeats a label.

Carrier-accounting mini case

A pure silicon sample receives donor atoms. Draw a neutral lattice-level sketch, state that donor levels make electrons easier to excite, identify electrons as majority carriers and holes as minority carriers, and explain why the whole sample remains electrically neutral. Repeat for acceptor doping with holes as majority carriers. Do not say that an n-type crystal is negatively charged or that a p-type crystal contains no electrons.

Finish with a two-column self-test. In the left column write claim cards such as “doping changes carrier concentration,” “a hole behaves as a positive mobile carrier,” and “conductivity depends on available states and carriers.” In the right column supply a diagram, mechanism or observable consequence. Mark an answer correct only if the evidence supports the claim. This evidence-first routine strengthens explanation questions, makes diagrams meaningful and exposes weak vocabulary before a timed test.

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