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Leaving Cert Physics: Semiconductors

How often Semiconductors comes up on the Physics papers, every year it was asked, and questions to try.

HL Asked on 8 of the last 10 Higher Level papers, most recently in 2025. most years

OL Asked on 6 of the last 10 Ordinary Level papers, most recently in 2026. most years

June 2027 is the first exam on the new Physics course. These come from the 2016–2026 papers, so read them as a guide.

Semiconductors, Higher Level(7 marks)

Quick ones on Semiconductors.

(a)Which impurity is added to make an n-type semiconductor?
  1. A trivalent element such as boron
  2. A pentavalent element such as phosphorus
  3. An inert gas such as argon
(b)What are the majority charge carriers in a p-type semiconductor?
  1. Protons
  2. Electrons
  3. Holes
(c)A transistor is used as a switch. What must happen for its collector current to flow?
  1. A small base current must flow
  2. The emitter must be disconnected
  3. The base must be disconnected
Show the answers

(a) A pentavalent element such as phosphorus

(b) Holes

(c) A small base current must flow

Your turn: Higher Level questions on Semiconductors.

Higher Level

Asked on 8 of the last 10 Higher Level papers, most recently in 2025. most years

Every paper, year by year

YearWhere it came up
2026Not asked
2025Q6(j)
2024Q9
2023Q5
2022Q8
2021Q6(j)
2019Q4, Q12(b)
2018Q12(d)
2017Not asked
2016Q8

Links open the State Examinations Commission’s paper for that year.

More Semiconductors questions

Semiconductors, 3 marks

What is a semiconductor?

  1. A material whose resistance lies between that of a conductor and an insulator and rises as temperature rises
  2. A material that conducts in one direction only and has no resistance in that direction
  3. A material whose resistance lies between that of a conductor and an insulator and falls as temperature rises
Show the answer

A material whose resistance lies between that of a conductor and an insulator and falls as temperature rises

Heating frees more charge carriers, so the resistance falls, which is the opposite of a metal. Silicon and germanium are the common examples.

Semiconductors, 3 marks

When does a p-n junction diode conduct?

  1. Only when alternating current is applied across both of its terminals
  2. When it is forward biased, with the p-side joined to the positive terminal
  3. When it is reverse biased, with the n-side joined to the positive terminal
Show the answer

When it is forward biased, with the p-side joined to the positive terminal

Forward bias narrows the depletion layer so current flows. Reverse bias widens it and almost no current flows, which is why diodes are used to rectify ac.

Semiconductors, 3 marks

In an automatic night light the LDR is in the lower arm of a potential divider feeding a transistor. Why does the lamp come on in the dark?

  1. The LDR's resistance rises, so the base voltage rises and the transistor switches on
  2. The LDR produces its own current in the dark, which switches the transistor on
  3. The LDR's resistance falls, so the base voltage rises and the transistor switches on
Show the answer

The LDR's resistance rises, so the base voltage rises and the transistor switches on

In the dark the LDR's resistance is high, so it takes a bigger share of the supply voltage. Once the base passes about 0.7 V the transistor turns on.

Ordinary Level

Asked on 6 of the last 10 Ordinary Level papers, most recently in 2026. most years

Every paper, year by year

YearWhere it came up
2026Q6(k)
2025Q6(i)
2024Q14(b)
2023Not asked
2022Not asked
2021Q6(j)
2019Q5(i)
2018Q5(d)
2017Not asked
2016Not asked

Links open the State Examinations Commission’s paper for that year.

More Semiconductors questions

Semiconductors, 2 marks

Which of these is a semiconductor?

  1. Copper
  2. Glass
  3. Silicon
Show the answer

Silicon

Silicon and germanium are semiconductors, with resistance between a conductor (copper) and an insulator (glass).

Semiconductors, 2 marks

What does a diode do in a circuit?

  1. It makes the current in the circuit larger
  2. It lets current flow in one direction only
  3. It stores charge and releases it later
Show the answer

It lets current flow in one direction only

A diode conducts when forward biased and blocks the current when reverse biased. It can be used to change ac to dc.

Semiconductors, 2 marks

How does the resistance of a light dependent resistor (LDR) change as the light gets brighter?

  1. It decreases
  2. It increases
  3. It stays the same
Show the answer

It decreases

More light frees more charge carriers in an LDR, so its resistance falls. LDRs are used to switch on street lights at night.

Other Physics topics

All of Leaving Cert Physics