An ideal transformer has 50 turns in its primary and 250 turns in its secondary. 12 Vac is connected to the primary. Find: (a) volts ac available at the second- ary; (b) current in a 1O-ohm device connected to the secondary; and (c) power supplied to the primary.

a. 60 V b. 6 A c. 360 W

Explanation:

a. Voltage in secondary

For an ideal transformer,

N₁/N₂ = I₂/I₁ = V₁/V₂ where N₁ = turns in primary = 50 turns, N₂ = turns in secondary = 250 turns, V₁ = voltage in primary = 12 V, V₂ = voltage in secondary = ? V

N₁/N₂ = V₁/V₂

V₂ = V₁N₂/N₁ = 250 × 12/50 = 60 V

b. Since V₂ = I₂R,

I₂ = V₂/R  R = 10 Ω

I₂ = 60 V/10 Ω

I₂ = 6 A

c. We first calculate the current in the primary from

N₁/N₂ = I₂/I₁  where I₁ = primary current

I₁ = N₂I₂/N₁ = 250 × 6 A/50 = 30 A

The power supplied to the primary is thus

P = I₁V₁ = 30 A × 12 V = 360 W