Which of the following can be described as high tension transmission?

Analysis

The question asks for the characteristics of "high tension" (HT) transmission lines, which are the large power lines you see on tall metal pylons across the country. To understand this, we must look at how electrical power is transmitted from power stations to our homes.

Concept: Power Transmission

Electrical power ($P$) is transmitted using the formula:

Where:

• $P$ is the power (measured in Watts)
• $I$ is the current (measured in Amperes)
• $V$ is the voltage (measured in Volts)

Power stations generate a fixed amount of power. To minimize energy loss due to heat (which occurs in the wires according to the formula $H = I^2Rt$), power companies want to keep the current ($I$) as low as possible.

Since $P = IV$, if we want to keep $P$ constant while making $I$ very small, we must make $V$ (the voltage) very large. This is why it is called "High Tension" or "High Voltage" transmission.

Step-by-Step Solution

1. Identify the goal: The goal of long-distance power transmission is to reduce energy loss in the cables.
2. Analyze the heat loss: Energy loss in cables is given by $P_{loss} = I^2R$. To minimize this, $I$ must be kept as low as possible.
3. Apply the power formula: Since $P = IV$, to transmit the same amount of power ($P$) with a very low current ($I$), the voltage ($V$) must be stepped up to a very high value.
4. Conclusion: High tension transmission is characterized by high voltage to allow for low current, which prevents the wires from overheating and losing energy.

Correct Option

Comparing this to your options:

• A is incorrect because high resistance would cause massive energy loss.
• B is correct because it describes the high voltage and low current required for efficient transmission.
• C is incorrect because high current would cause the wires to melt or lose too much energy.
• D is incorrect because high current is the opposite of what is needed for high tension.

Exam Tip: Always remember the phrase "Step-up to save." Transformers "step up" the voltage to a high level so that the current is "stepped down" to a low level, saving energy during transmission.