# High Voltage Low current from a step up transformer

• john liang
In summary, the lightbulbs connected in series will have the same voltage and current, while those connected in parallel will have different voltages and currents.
john liang
Hi,

From what I have read, if a bulb X is connected to the input voltage of a step-up transformer, and another similar bulb Y is connected to the output voltage (secondary coil), then Y will be brighter than X.

From Joule's law of P = V I, it seems that the output voltage will be higher and the current will be lower.

My question is, if the current in the secondary coil is lower, how come the bulb Y is brighter?

Thanks.

The current in the secondary is not a given quantity. It's determined by the voltage E and the resistance R of the bulb. Therefore the correct form of Joule's Law to use is P = E2/R, showing that the power increases as the voltage is increased.

The current in the secondary is not a given quantity. It's determined by the voltage E and the resistance R of the bulb. Therefore the correct form of Joule's Law to use is P = E2/R, showing that the power increases as the voltage is increased. - Bill_K

Isn't it a fact that if the output voltage of the secondary coil is say 5x higher than the input voltage of the primary coil, the output current is 1/5 of the input current?
Thanks

Welcome to Physics Forums.

The current in the primary coil is different than the current in the lightbulb connected across it. They are in parallel with each other, so they have the same voltage but not (necessarily) the same current.

Therefore, your correct statement about the relative currents in the primary and secondary does not apply to the currents in the lightbulbs.

The current in the secondary is variable depending on the load connected to it. The maxim current the secondary can supply is 1/5 of the input current. The input current is also variable and depends on how the transformer is loaded. You need to go back to E = IR and understand how current changes with load.

## 1. What is a step up transformer?

A step up transformer is a type of electrical transformer that is used to increase the voltage of an alternating current (AC) electricity supply.

## 2. How does a step up transformer work?

A step up transformer works by using two coils of wire, known as the primary and secondary windings, that are wrapped around a shared iron core. When an alternating current flows through the primary winding, it creates a changing magnetic field in the core. This changing magnetic field induces a voltage in the secondary winding, resulting in a higher output voltage.

## 3. What is considered high voltage and low current?

High voltage is typically defined as any voltage above 1000 volts, while low current is typically considered to be below 1 ampere. However, the exact definitions may vary depending on the specific application and industry.

## 4. What are some common uses for a step up transformer?

A step up transformer is commonly used in power transmission systems to increase the voltage of electricity for efficient long-distance transmission. It is also used in electronic devices to convert low voltage AC to higher voltage AC, such as in power adapters for laptops and smartphones.

## 5. What are the potential dangers of working with high voltage low current from a step up transformer?

Working with high voltage can be extremely dangerous, as it can cause electric shock, burns, and even death. It is important to always follow safety procedures and use proper protective equipment when working with high voltage. Additionally, there may be risks of fire or damage to equipment if the transformer is not used properly or if there is a fault in the system.

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