Question 4 of 9intermediate🔧 ApplyShort Answer2 marks

Suppose the '+' and '–' symbols cannot be read on a battery. Suggest a method to identify the two terminals of this battery.

Correct Answer

To identify the positive and negative terminals of a battery without symbols, use an LED.

Connect the LED to the battery using two wires. The LED has two wires of different lengths—the longer wire is the positive terminal and the shorter wire is the negative terminal.

Connect the LED to the battery in one direction. If the LED glows, then the terminal connected to the longer wire of the LED is the positive terminal of the battery, and the terminal connected to the shorter wire is the negative terminal.

If the LED does not glow, reverse the connections. The LED will glow only when connected with correct polarity, thus identifying the battery terminals.

Exercise: Let Us Enhance Our Learning | Q: 9 | (Page Page 17)
For More Understanding

Explanation

The chapter explains on page 5 that 'LEDs... have two terminals, but one is positive (attached to a longer wire) and the other is negative (the shorter wire).' On page 9, it states that 'The current passes through the LED only when the positive terminal (longer wire) of the LED is connected to the positive terminal of the battery, and negative terminal (shorter wire) of the LED is connected to the negative terminal of the battery.' This property of LEDs can be used to identify the polarity of an unmarked battery.

Solution Steps

  1. Use an LED to test the battery terminals

  2. Identify the LED terminals: longer wire is positive, shorter wire is negative

  3. Connect the LED to the battery in one direction

  4. If the LED glows, the battery terminal connected to the longer wire is positive

  5. If the LED does not glow, reverse the connections

  6. The LED glows only when connected with correct polarity

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