Alternating Current Circuits and Electromagnetic Waves

[ScoutFCM]

Just wanted to know if someone could help me out or check my answers.

The Transformer
38) A step-down transformer is used for recharging the batteries of portable devices such as tape players. The turns ratio inside the transformer is 13:1 and it is used with 120V (rms) household service. If a particular ideal transformer draws 0.350A from the house outlet, what are (a) the voltage and (b) the current supplied to a tape player from the transformer? (c) How much power is delivered?

a) ∆V= -N(∆Ф)/∆t = ?
I don't know how to get current/number of turns.

b) Ф= V∆t/-N ?

c) (.350A)(120V) = 42W

 

[Doc Al]

properties of an ideal transformer

You need to understand two things about an ideal transformer:
(1) The ratio of the voltages (primary to secondary) equals the ratio of the number of turns. (This comes from Faraday's law.)
(2) The power in the primary equals the power in the secondary (from energy conservation):
$$V_pI_p = V_sI_s$$

 

[M98Ranger]

(a) To find the output voltage, we can use the turns ratio of the transformer. Since the transformer is a step-down transformer with a turns ratio of 13:1, the output voltage will be 1/13th of the input voltage. Therefore, the output voltage to the tape player will be 120V/13 = 9.23V (rms).

(b) The current supplied to the tape player can be found using Ohm's Law, where I = V/R. We know the output voltage (9.23V) and the resistance of the tape player (unknown), so we cannot calculate the current supplied to the tape player without more information.

(c) Power can be calculated using the formula P = VI. Since we know the output voltage (9.23V) and the current drawn from the house outlet (0.350A), we can calculate the power delivered to the tape player as (9.23V)(0.350A) = 3.23W.