Q6 of 16 Page 14

What is LED? Why it can be used in place of a bulb in the tester?

We may use a LED in place of electric bulb. LED glows even when a small electric current flows through it. There are two wires (called leads) attached to LED. One lead is slightly longer than the other one. Remember that while connecting a circuit the longer lead of LED is always connected to the positive of the battery and the shorter lead is connected to the negative terminal of battery.

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4 Give some examples of insulators. 5 In previous class you have used a tester as shown is figure given below to test whether electric current passed through a particular material or not? When this tester is used for liquids sometimes even though the liquid allows the electric current to pass and the circuit is complete, bulb does not glow. What can be the reason? 7 How the magnetic effect of current can be used to detect current? 8 Using the tester made is Q. 7 test the conductivity of liquids such as tap water, vegetable oil, milk, kerosene etc. and complete table: 


S. No Material Compass needle shows deflection Yes/No Conductor/Insulator
1. Lemon Juice Yes Conductor
2. Vinegar   
3. Tap water   
4. Vegetable oil   
5. Milk   
6. Honey