What is a Transformer (physics)?

S4-SA1-0684

Grade Level:

Class 7

Space Technology, EVs, Climate Change, Biotechnology, HealthTech, Robotics, Chemistry, Physics

Definition

What is it?

A transformer is an electrical device that changes the voltage of alternating current (AC) electricity. It can either increase the voltage (step-up transformer) or decrease it (step-down transformer) without changing the frequency.

Simple Example

Quick Example

Imagine you have a mobile phone charger. The electricity coming from your home socket is too high (around 230V) for your phone. The charger has a small transformer inside that 'steps down' this high voltage to a much lower, safe voltage (like 5V or 9V) that your phone can use to charge its battery.

Worked Example

Step-by-Step

Let's say a power station produces electricity at 11,000 Volts. To send this electricity over long distances, we need to increase the voltage to reduce power loss.

1. A step-up transformer at the power station has a primary coil with 100 turns and a secondary coil with 1000 turns.
2. The input voltage (Vp) is 11,000V.
3. We want to find the output voltage (Vs).
4. The formula for a transformer is Vs/Vp = Ns/Np, where Ns is turns in secondary coil and Np is turns in primary coil.
5. So, Vs / 11,000V = 1000 / 100.
6. Vs / 11,000V = 10.
7. Vs = 10 * 11,000V.
8. Vs = 110,000V.

ANSWER: The output voltage will be 110,000 Volts.

Why It Matters

Transformers are crucial for delivering electricity to our homes and powering everything from our fans to our laptops. They are essential in electric vehicles (EVs) for charging and managing battery power, and in space technology to power satellites. Electrical engineers and power grid operators use transformers daily to ensure stable electricity supply.

Common Mistakes

MISTAKE: Thinking transformers work with direct current (DC) electricity. | CORRECTION: Transformers only work with alternating current (AC) because they rely on changing magnetic fields.

MISTAKE: Believing a transformer creates electrical energy. | CORRECTION: A transformer only changes the voltage and current, it does not create energy. The total power remains nearly the same (ignoring small losses).

MISTAKE: Confusing step-up and step-down transformers based on coil size. | CORRECTION: A step-up transformer has more turns in its secondary coil than its primary coil, increasing voltage. A step-down transformer has fewer turns in its secondary coil, decreasing voltage.

Practice Questions

Try It Yourself

QUESTION: A step-down transformer has 500 turns in its primary coil and 50 turns in its secondary coil. If the input voltage is 230V, what is the output voltage? | ANSWER: 23V

QUESTION: A transformer is used to increase voltage from 100V to 1000V. If the primary coil has 200 turns, how many turns must the secondary coil have? | ANSWER: 2000 turns

QUESTION: Why are transformers essential for transmitting electricity from power plants to our homes over long distances, and what type of transformer is used at the power plant for this purpose? | ANSWER: Transformers are essential because they allow voltage to be increased for long-distance transmission, which reduces power loss. A step-up transformer is used at the power plant.

MCQ

Quick Quiz

What kind of current does a transformer primarily work with?

Direct Current (DC)

Alternating Current (AC)

Both DC and AC

Pulsating Current

The Correct Answer Is:

Transformers rely on the principle of electromagnetic induction, which requires a changing magnetic field. This changing magnetic field is produced only by alternating current (AC), not direct current (DC).

Real World Connection

In the Real World

Next time you see those tall electricity poles with big grey boxes on them in your neighbourhood or near a railway track, you're likely looking at a transformer! These boxes 'step down' the high voltage electricity from power lines to a safer voltage that can be used in your homes and shops. This ensures that the electricity supplied to your home appliances like refrigerators and TVs is at the correct and safe voltage.

Key Vocabulary

Key Terms

VOLTAGE: The electrical 'push' or pressure that makes current flow | ALTERNATING CURRENT (AC): Electric current that periodically reverses direction | PRIMARY COIL: The coil of a transformer to which the input voltage is applied | SECONDARY COIL: The coil of a transformer from which the output voltage is taken | STEP-UP TRANSFORMER: A transformer that increases voltage

What's Next

What to Learn Next

Now that you understand how transformers change voltage, you can explore how electricity is generated in power plants and how it travels through the entire power grid to reach your home. This will help you appreciate the journey of the electricity you use every day!