A step-up transformer must increase the voltage fivefold. What must be the ratio of secondary coil turns to primary coil turns?

1. The transformer equation states that the ratio of secondary to primary voltage equals the ratio of secondary to primary turns (Vs/Vp = Ns/Np). 2. The transformer needs to increase voltage fivefold, so Vs/Vp = 5. 3. By the transformer equation, Ns/Np must also equal 5, i.e. a 5:1 ratio of secondary to primary turns. 4. 1:5 would step the voltage down, not up; 25:1 and 10:1 do not match a simple fivefold increase. 5. So the secondary coil needs 5 times as many turns as the primary coil. _Source: OpenStax Physics Ch 20 "Magnetism", p.690 §20.2 Motors, Generators, and Transformers_