Conductor vs Semiconductor — Difference (with Table & FAQs)
Conductor vs Semiconductor compared side by side — a 5-row comparison table, 4 key points and 7 exam FAQs. Class 10 Physics, free and no sign-up.
TL;DR: Conductor vs Semiconductor compared side by side — a 5-row comparison table, 4 key points and 7 exam FAQs. Class 10 Physics, free and no sign-up.
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
The main difference between Conductor and Semiconductor: Conductors allow electricity to flow freely while semiconductors have limited conductivity. Semiconductors are crucial for modern electronics studied in CB
Conductor vs Semiconductor — Comparison Table
| Basis | Conductor | Semiconductor |
|---|---|---|
| Conductivity | Very high | Moderate |
| Resistance | Very low | Medium |
| Free electrons | Many free electrons | Few free electrons |
| Temperature effect | Conductivity decreases with heat | Conductivity increases with heat |
| Examples | Copper, aluminum, silver | Silicon, germanium |
Key Points
- Conductors are used for wiring electricity
- Semiconductors are used in transistors and diodes
- Purity affects semiconductor conductivity
- Semiconductors can be doped to change properties
Conductors — electrons are already free
A conductor is a material through which electric current flows easily, because it contains a very large number of free electrons that are not bound to any one atom. Apply even a small voltage and those electrons drift, producing a current.
Conductors have very low resistivity, of the order of 10⁻⁸ to 10⁻⁶ ohm-metre. Silver is the best conductor, but copper and aluminium are used in practice because they are far cheaper. Their resistance increases as temperature rises: the atoms vibrate more vigorously, the drifting electrons collide with them more often, and the flow is impeded.
Semiconductors — conductivity you can control
A semiconductor has a conductivity between that of a conductor and an insulator, with resistivity roughly 10⁻⁵ to 10⁶ ohm-metre. Silicon and germanium are the standard examples, both from group 14 with four valence electrons.
Their defining behaviour is the opposite of a conductor's: the resistance of a semiconductor decreases as temperature rises. Heat frees more electrons from their covalent bonds, so more charge carriers become available. This is described as a negative temperature coefficient of resistance, and it is the single most examined contrast in the topic.
Band theory — the reason for the difference
Energy-band structure explains in one picture why these materials behave so differently.
- In a conductor the valence band and the conduction band overlap, or the conduction band is partly filled. Electrons need almost no extra energy to move, so current flows freely.
- In a semiconductor there is a small forbidden energy gap between the bands — about 1.1 eV for silicon and 0.7 eV for germanium. At absolute zero a pure semiconductor behaves as an insulator; at room temperature some electrons gain enough thermal energy to jump the gap.
- In an insulator the forbidden gap is large, typically more than 3 eV, so under ordinary conditions almost no electrons can cross it and virtually no current flows.
- When an electron leaves the valence band it leaves behind a vacancy called a hole, which behaves as a positive charge carrier. Semiconductors therefore conduct by both electrons and holes; conductors conduct by electrons alone.
Doping — why semiconductors are so useful
A pure (intrinsic) semiconductor is not very useful on its own. Adding a tiny, controlled amount of impurity — a process called doping — raises its conductivity enormously and lets engineers decide which kind of charge carrier dominates. The doped material is called an extrinsic semiconductor.
Adding a pentavalent impurity (five valence electrons: phosphorus, arsenic or antimony) leaves one spare electron per atom. Electrons become the majority carriers, and the result is an n-type semiconductor.
Adding a trivalent impurity (three valence electrons: boron, aluminium or gallium) leaves one bond short, creating a hole. Holes become the majority carriers, and the result is a p-type semiconductor. Joining a p-type and an n-type piece makes a p-n junction — the diode, and the foundation of every transistor, integrated circuit and solar cell.
Where each is used
Conductors are used wherever current simply has to be carried: copper wiring in homes, aluminium in overhead transmission lines, and the metal filaments and contacts inside appliances.
Semiconductors are used wherever current has to be controlled rather than merely carried: diodes, transistors, LEDs, integrated circuits, solar cells and thermistors. This is the practical difference — conductors transport electricity, semiconductors switch and amplify it.
Conductor vs Semiconductor — Worked Examples
- Copper household wiring — A conductor. It has abundant free electrons and very low resistivity, so it carries current with little loss.
- A silicon chip in a phone — A semiconductor. Its conductivity is controlled by doping, allowing millions of switches on one wafer.
- A wire getting hotter and its resistance rising — Conductor behaviour — a positive temperature coefficient.
- A thermistor whose resistance falls when heated — Semiconductor behaviour — a negative temperature coefficient, which is what makes it useful as a temperature sensor.
Common Mistakes Students Make
- Saying the resistance of a semiconductor increases with temperature. It decreases — this is the opposite of a conductor.
- Describing a semiconductor as simply 'a weak conductor'. Its usefulness comes from being controllable by doping, not from its raw conductivity.
- Forgetting that semiconductors conduct by holes as well as electrons.
- Thinking doping makes the semiconductor electrically charged. The material stays neutral overall; doping only changes which carrier is in the majority.
- Mixing up n-type and p-type. Pentavalent impurity gives n-type (extra electrons); trivalent gives p-type (holes).
Diagrams
Where This Shows Up in Real Life
Why transmission lines are aluminium, not copper
Copper conducts better, but aluminium is far lighter and much cheaper, and for overhead lines strung between pylons weight decides the engineering. Household wiring uses copper because the runs are short and conductivity matters more than mass. Silver is the best conductor of all and is used only where cost is irrelevant, such as in specialised contacts.
The thermistor in your appliances
A thermistor is a semiconductor whose resistance falls sharply as temperature rises. That behaviour, the opposite of a metal, makes it an excellent temperature sensor: measure the resistance and you know the temperature. Thermistors sit inside refrigerators, air conditioners, ovens and battery packs, and they exist precisely because of the negative temperature coefficient that defines a semiconductor.
Why solar panels are silicon
A photon with enough energy can lift an electron across silicon’s 1.1 eV band gap, creating a free electron and a hole. A p-n junction then separates them and drives a current through an external circuit. A conductor cannot do this — its bands overlap, so there is no gap to cross and no way to convert light into a directed current. The band gap is not a defect; it is the entire mechanism.
Doping is what makes modern electronics possible
Adding roughly one impurity atom per million silicon atoms can raise conductivity enormously and decide whether electrons or holes carry the current. That controllability is why a semiconductor can switch and amplify while a conductor can only carry. Every transistor, integrated circuit, LED and microprocessor rests on it.
Solved Numericals — Step by Step
Problem 1. Calculate the resistance of a copper wire of length 2 m and cross-sectional area 1 × 10⁻⁶ m², given resistivity 1.7 × 10⁻⁸ Ω m.
- R = ρL ÷ A.
- R = (1.7 × 10⁻⁸ × 2) ÷ (1 × 10⁻⁶)
- = (3.4 × 10⁻⁸) ÷ (1 × 10⁻⁶)
- = 3.4 × 10⁻².
Answer: 0.034 Ω. The very low resistivity of a conductor is why such a wire offers almost no resistance.
Problem 2. A silicon sample has a band gap of 1.1 eV. Express this energy in joules. (1 eV = 1.6 × 10⁻¹⁹ J)
- Energy in joules = energy in eV × 1.6 × 10⁻¹⁹.
- = 1.1 × 1.6 × 10⁻¹⁹
- = 1.76 × 10⁻¹⁹ J.
Answer: 1.76 × 10⁻¹⁹ J. Any photon carrying at least this much energy can free an electron in silicon.
Board-Style Questions with Model Answers
Distinguish between conductors, semiconductors and insulators on the basis of energy bands and resistivity. (5 marks)
In a conductor the valence band and the conduction band overlap, or the conduction band is only partly filled, so electrons need virtually no additional energy to move and current flows freely. Resistivity is very low, of the order of 10⁻⁸ to 10⁻⁶ ohm metre, and examples are silver, copper and aluminium. In a semiconductor there is a small forbidden energy gap between the two bands, about 1.1 eV in silicon and 0.7 eV in germanium. At absolute zero a pure semiconductor behaves as an insulator, but at room temperature thermal energy lifts some electrons across the gap. Resistivity lies between roughly 10⁻⁵ and 10⁶ ohm metre. In an insulator the forbidden gap is large, generally above 3 eV, so under ordinary conditions almost no electrons can cross it and virtually no current flows; resistivity exceeds about 10⁸ ohm metre, and examples are rubber and glass.
Why does the resistance of a conductor increase with temperature while that of a semiconductor decreases? (3 marks)
In a conductor the number of free electrons is already very large and does not change appreciably with temperature. Heating simply makes the lattice atoms vibrate more vigorously, so the drifting electrons collide with them more frequently, their motion is impeded, and the resistance rises. A conductor therefore has a positive temperature coefficient of resistance. In a semiconductor the number of charge carriers is small at room temperature and depends strongly on temperature. Heating supplies energy that lifts additional electrons across the small forbidden gap into the conduction band, creating both free electrons and holes. This large increase in the number of carriers far outweighs the increased collisions, so the net resistance falls. A semiconductor therefore has a negative temperature coefficient of resistance.
What is doping? Distinguish between n-type and p-type semiconductors. (5 marks)
Doping is the deliberate addition of a very small, controlled quantity of a suitable impurity to a pure semiconductor in order to increase its conductivity greatly and to determine which kind of charge carrier predominates. The resulting material is called an extrinsic semiconductor. An n-type semiconductor is produced by adding a pentavalent impurity such as phosphorus, arsenic or antimony, which has five valence electrons. Four form covalent bonds with the surrounding silicon atoms and the fifth is left loosely bound and easily freed, so electrons become the majority carriers and holes the minority carriers. A p-type semiconductor is produced by adding a trivalent impurity such as boron, aluminium or gallium, which has only three valence electrons. One bond is left incomplete, creating a hole, so holes become the majority carriers and electrons the minority carriers. In both cases the material remains electrically neutral overall, because no net charge has been added.
What is a hole? Explain how it contributes to conduction. (3 marks)
When an electron gains enough energy to leave its position in a covalent bond and move into the conduction band, it leaves behind a vacancy in the valence band. This vacancy is called a hole, and because the absence of a negative charge leaves a local excess of positive charge, a hole behaves as a positive charge carrier. Conduction occurs when a neighbouring valence electron moves into the hole, filling it but creating a new hole at its own former position. Repeated many times, this makes the hole appear to travel through the material in the direction opposite to the movement of the electrons. A semiconductor therefore conducts by both electrons and holes, whereas a conductor conducts by free electrons alone.
Assertion–Reason Questions (CBSE Format)
For each question choose: (a) both A and R are true and R is the correct explanation of A; (b) both are true but R is not the correct explanation; (c) A is true but R is false; (d) A is false but R is true.
1. Assertion (A): The resistance of a semiconductor decreases as temperature increases.
Reason (R): Heating frees additional electrons across the small forbidden energy gap.
Answer: (a) — Both are true and the reason explains the assertion. The increase in charge carriers outweighs the increased lattice collisions.
2. Assertion (A): A pure semiconductor behaves as an insulator at absolute zero.
Reason (R): At absolute zero no electron has enough thermal energy to cross the forbidden gap.
Answer: (a) — Both are true and correctly linked. The conduction band is empty, so no current can flow.
3. Assertion (A): An n-type semiconductor carries a net negative charge.
Reason (R): Electrons are the majority carriers in an n-type semiconductor.
Answer: (d) — The assertion is false — the material stays electrically NEUTRAL, since each donor atom contributes a positive nucleus along with its extra electron. The reason is true and is precisely the fact students misread as implying net charge.
4. Assertion (A): Silicon is preferred over germanium in most devices.
Reason (R): Silicon has a larger band gap and so is less affected by temperature.
Answer: (a) — Both are true and correctly linked. Silicon’s 1.1 eV gap against germanium’s 0.7 eV gives better high-temperature stability, and silicon is also cheaper and more abundant.
Quick Self-Check
Q1. When temperature increases, the resistance of a semiconductor:
- A. Increases
- B. Decreases
- C. Stays constant
- D. Becomes infinite
Answer: B. Decreases — Heat frees more electrons across the small forbidden gap, creating more charge carriers, so resistance falls. Conductors behave the opposite way.
Q2. Doping silicon with phosphorus produces:
- A. p-type semiconductor
- B. n-type semiconductor
- C. An insulator
- D. A conductor
Answer: B. n-type semiconductor — Phosphorus is pentavalent, so it contributes a spare electron. Electrons become the majority carriers, giving n-type.
Q3. The forbidden energy gap in silicon is approximately:
- A. 0 eV
- B. 1.1 eV
- C. 3 eV
- D. 6 eV
Answer: B. 1.1 eV — Silicon's band gap is about 1.1 eV and germanium's about 0.7 eV. Insulators have gaps above roughly 3 eV.
Q4. In a conductor, the valence and conduction bands:
- A. Are separated by a large gap
- B. Overlap or are partly filled
- C. Are both empty
- D. Are separated by 1.1 eV
Answer: B. Overlap or are partly filled — Overlapping or partly filled bands mean electrons need almost no extra energy to move, which is why conductors conduct freely.
Key Terms Glossary
- Conductor
- A material with abundant free electrons and very low resistivity (10⁻⁸ to 10⁻⁶ Ω m). Copper, aluminium, silver.
- Semiconductor
- A material whose conductivity lies between a conductor and an insulator, controllable by doping. Silicon, germanium.
- Insulator
- A material with a forbidden gap above about 3 eV, so almost no current flows. Rubber, glass.
- Valence band
- The energy band containing the outermost bound electrons of the atoms.
- Conduction band
- The energy band in which electrons are free to move and carry current.
- Forbidden energy gap
- The energy separation between valence and conduction bands. ~1.1 eV in silicon, ~0.7 eV in germanium.
- Hole
- The vacancy left when an electron leaves a covalent bond. Behaves as a positive charge carrier.
- Doping
- Adding a controlled trace impurity to raise conductivity and set the majority carrier.
- n-type
- Doped with a PENTAVALENT impurity (phosphorus, arsenic). ELECTRONS are the majority carriers.
- p-type
- Doped with a TRIVALENT impurity (boron, gallium). HOLES are the majority carriers.
- Intrinsic semiconductor
- A pure, undoped semiconductor with equal numbers of electrons and holes.
- Negative temperature coefficient
- Resistance FALLS as temperature rises — the defining behaviour of a semiconductor.
One-Minute Revision
- CONDUCTOR: bands OVERLAP, resistivity 10⁻⁸-10⁻⁶ Ω m, resistance RISES with temperature.
- SEMICONDUCTOR: small gap (~1.1 eV Si, 0.7 eV Ge), resistance FALLS with temperature.
- INSULATOR: gap > 3 eV, effectively no conduction.
- The temperature reversal is THE most-examined contrast in this topic.
- Semiconductors conduct by ELECTRONS **and** HOLES. Conductors use electrons only.
- PENTAVALENT doping (P, As) → n-type, electrons majority. TRIVALENT (B, Ga) → p-type, holes majority.
- Doping does NOT charge the material — it stays electrically neutral overall.
- Silicon beats germanium: larger gap, better heat stability, cheaper, forms a usable oxide.
Syllabus reference: NCERT Class 10 Science, Chapter 11 — Electricity; band theory and doping in Class 12 Physics, Chapter 14 — Semiconductor Electronics.
Frequently Asked Questions
What is the difference between a conductor and a semiconductor?
A conductor (like copper) lets electric current flow easily because it has many free electrons. A semiconductor (like silicon) conducts only partially — its conductivity lies between that of a conductor and an insulator.
Give examples of conductors and semiconductors.
Conductors: copper, aluminium, silver, iron. Semiconductors: silicon and germanium.
How does temperature affect a semiconductor?
Unlike a metal conductor, a semiconductor’s conductivity increases as temperature rises, because more electrons become free to move.
Why does a semiconductor's resistance fall when heated but a conductor's rise?
In a conductor the number of free electrons is already fixed and very large; heating only makes the atoms vibrate more, so electrons collide more often and resistance rises. In a semiconductor heating actually creates new charge carriers by freeing electrons across the small band gap, and that increase outweighs the extra collisions, so resistance falls.
What is a hole in a semiconductor?
When an electron leaves its place in a covalent bond, it leaves a vacancy that behaves like a positive charge carrier. This vacancy is called a hole. Neighbouring electrons move into it, so the hole appears to move in the opposite direction to the electrons, contributing to the current.
What is the difference between intrinsic and extrinsic semiconductors?
An intrinsic semiconductor is pure, with equal numbers of electrons and holes and low conductivity. An extrinsic semiconductor has been deliberately doped with a small impurity, which greatly increases its conductivity and makes either electrons (n-type) or holes (p-type) the majority carriers.
Why is silicon preferred over germanium?
Silicon has a larger band gap (1.1 eV against 0.7 eV), so it is much less affected by heat and works reliably at higher temperatures. It is also far more abundant, cheaper, and forms a stable oxide layer that is essential for manufacturing integrated circuits.