The charger for your cell phone contains a small...

The charger for your cell phone contains a small transformer. While charging, it provides $5.0 \mathrm{W}$ to your phone at $5.0 \mathrm{V}$. Assuming an ideal transformer, how much current does this transformer draw from the $120 \mathrm{V}$ wall socket?

Key Concepts

Alternating Current (AC) Supply

An AC supply provides a voltage that alternates in polarity over time, and is typically used in household power systems, such as a 120 V mains supply. Understanding AC characteristics is important for analyzing transformers because they are commonly used to step down or step up voltage levels in AC circuits without altering the frequency.

Voltage, Current, and Power Relationship

The relationship between voltage, current, and power in electrical circuits is given by the formula P = V × I. This fundamental equation allows one to calculate any one of the three quantities if the other two are known. In transformer calculations, this relationship is used in conjunction with the conservation of energy principle to relate the input and output current and voltage parameters.

Ideal Transformer

An ideal transformer is a theoretical device that transfers electrical energy between two or more circuits through electromagnetic induction without any energy losses. It assumes perfect coupling between the coils and no resistive losses, which means the power input to the transformer equals the power output. This concept is crucial for simplifying the analysis of transformer operations in circuits.

Conservation of Energy

In the context of an ideal transformer, the conservation of energy principle states that the power delivered to the secondary circuit is equal to the power drawn from the primary circuit. This means that any decrease in voltage is proportionally accompanied by an increase in current, ensuring that the total energy remains constant, a fundamental principle in electrical energy management.

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