why is the longer lead of LED is always connected to the positive terminal and shorter to the negetive terminal of the battery?
Your friends are correct.LED has two leads,The lead connected to the positive terminal of battery is called anode,and lead connected to the negative terminal is cathode.The slightly longer lead than the other is always connected to the positive terminalthe shorter lead is connected to the negative terminal.
If you connect an LED on its own to your battery, the battery will heat up the LED and destroy the LED. Try connecting one LED to the battery alone by plugging it right across the battery voltage. If you connect it one way, nothing happens, because the LED won't let electrons through that way. Connect it the other way around. Now it should shine and get warm. The correct way is with the long lead on the Positive Terminal and the short lead on the Negative Terminal. The LEDs will not explode.
On an LED device the longer leg is always the anode, and the shorter leg is the cathode. Current always flows from the anode to the cathode. In a simple circuit, the anode of the LED is connected to the positive voltage supply, and the cathode is connected to ground, or the negative voltage supply. A good way to remember the names using the schematic symbol is that “anode” and “arrow” both start with the letter “a”. So the side of the schematic symbol connected to the “arrow” is the “anode”, making the side connected to the line the cathode.
it is always necesssary to make sure that longer lead of LED is always connected to the positive terminal and shorter to the negetive terminal of the battery because current only flows from anode to cathode not from cathode to anode. as i already mentioned above anode is the positive terminal of the battery which is the longer leg. and cathode is the negative terminal, the shorter leg!