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Leaving Cert Technology: Ohm's law, resistors & power

How often Ohm's law, resistors & power comes up on the Technology papers, every year it was asked, and questions to try.

HL Asked on 9 of the last 9 Higher Level papers, most recently in 2025. banker

OL Asked on 7 of the last 9 Ordinary Level papers, most recently in 2025. most years

Ohm's law, resistors & power, Higher Level(7 marks)

Quick ones on Ohm's law, resistors & power.

(a)A 9 V supply is connected across a 450 Ω resistor. What current flows?
  1. 0.2 A (200 mA)
  2. 0.02 A (20 mA)
  3. 4050 A (4.05 kA)
(b)A resistor's bands are red, violet, orange, gold. What is its value?
  1. 2.7 kΩ ±5%
  2. 273 Ω ±5%
  3. 27 kΩ ±5%
(c)What is the total resistance of 220 Ω and 330 Ω in series?
  1. 550 Ω
  2. 110 Ω
  3. 132 Ω
Show the answers

(a) 0.02 A (20 mA)

(b) 27 kΩ ±5%

(c) 550 Ω

Your turn: Higher Level questions on Ohm's law, resistors & power.

Higher Level

Asked on 9 of the last 9 Higher Level papers, most recently in 2025. banker

Every paper, year by year

YearWhere it came up
2025A12, B2b
2024A5, A9
2023A3, B3c
2022A5, B3c
2021B3c
2019A14
2018A4, A6
2017A11, B3b
2016A6

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

More Ohm's law, resistors & power questions

Ohm's law, resistors & power, 3 marks

What are the first three bands of a 680 Ω resistor?

  1. Blue, grey, black
  2. Grey, blue, brown
  3. Blue, grey, brown
Show the answer

Blue, grey, brown

680 = 6, 8 then one zero. Blue is 6, grey is 8 and brown is the multiplier (x10). Blue, grey, black would be only 68 Ω.

Ohm's law, resistors & power, 2 marks

How is a voltmeter connected to measure the voltage across a resistor?

  1. In series with the supply only
  2. In parallel with the resistor
  3. In series with the resistor
Show the answer

In parallel with the resistor

A voltmeter measures the difference in voltage between two points, so it goes across (in parallel with) the part. Ammeters go in series.

Ohm's law, resistors & power, 3 marks

Three 60 Ω resistors are connected in parallel. What is the total resistance?

  1. 20 Ω
  2. 180 Ω
  3. 60 Ω
Show the answer

20 Ω

For equal resistors in parallel, total = R / n = 60 / 3 = 20 Ω. Parallel resistance is always less than the smallest single resistor.

Ordinary Level

Asked on 7 of the last 9 Ordinary Level papers, most recently in 2025. most years

Every paper, year by year

YearWhere it came up
2025A5, B2c
2024Not asked
2023B3b
2022A11, B3c
2021A8
2019A11
2018B3b, B3c
2017Not asked
2016A8

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

More Ohm's law, resistors & power questions

Ohm's law, resistors & power, 3 marks

6 V is applied across a 200 Ω resistor. What current flows?

  1. 1200 A
  2. 33.3 A
  3. 0.03 A
Show the answer

0.03 A

I = V ÷ R = 6 ÷ 200 = 0.03 A (30 mA). Rearrange V = IR for the unknown and keep the units in volts, amps and ohms.

Ohm's law, resistors & power, 3 marks

A resistor's bands are red, red, brown, gold. What is its value?

  1. 2200 Ω ± 5%
  2. 220 Ω ± 5%
  3. 22 Ω ± 5%
Show the answer

220 Ω ± 5%

Red = 2, red = 2, and the brown multiplier = ×10, so 22 × 10 = 220 Ω. The gold band gives a tolerance of ± 5%.

Ohm's law, resistors & power, 3 marks

A current of 0.02 A flows through a 470 Ω resistor. What is the voltage across it?

  1. 9.4 V
  2. 94 V
  3. 23 500 V
Show the answer

9.4 V

V = I × R = 0.02 × 470 = 9.4 V. Always change mA to A first: 20 mA = 0.02 A.

Other Technology topics

All of Leaving Cert Technology