The structure and action of a transformer, the turns-ratio equation, power in an ideal transformer, the features of the core, and why electricity is transmitted at high voltage.
5 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.
A phone charger takes 120 V from the wall and delivers 5 V to your phone. A transformer inside does the job with no moving parts.
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Change the turns and the voltage and read the output voltage.
Copy these into your notebook in your own words — that is how they stick.
Primary coil, secondary coil, laminated soft-iron core; works with a.c. only.
Soft iron (easily magnetised/demagnetised) and laminated (reduces eddy currents).
Alternating flux in the core induces an alternating e.m.f. in the secondary.
V_s/V_p = N_s/N_p.
N_s > N_p raises the voltage; N_s < N_p lowers it.
V_pI_p = V_sI_s.
High V, low I: less I²R heat loss.
Not 100% efficient: resistance of coils, eddy currents, flux leakage.
3 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness. More games in the Physics Arcade.
8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better. Work each item on paper first.
Write full answers, then reveal the mark scheme and tick the points you earned (16 marks in total). Show all your working — method marks count. Your answers are saved on this device.
Question 1 [16 marks]
A step-down transformer has 1 000 turns on the primary coil connected to a 120 V a.c. supply and an output of 9.0 V. A fuse is connected in series with the primary coil.
(a) (a) Explain what is meant by alternating current. [2]
(b) (b) State two features of the core and the reason for each. [4]
(c) (c) Describe how the output voltage is induced in the secondary coil. [3]
(d) (d) Calculate the number of turns on the secondary coil. [3]
(e) (e) State the function of the fuse in the primary circuit. [1]
(f) (f) The primary current is 0.20 A. Assuming the transformer is ideal, calculate the current in the secondary coil. [3]
Find these in your own past-paper booklets for extra timed practice. Items above are written in the style of these papers; any adapted from a specific question say so.