Class Activity (week two)

A piece of hot dog connected to a AC power supply. First, water inside of hot dog cased that current pass through hot dog easily, but current in hot dog made heat and caused water vaporize. Therefore, gradually water inside of hot dog finished, and current went down. 

Figure 1: Current - Time graph of Hot dog

Diodes are two-terminal semiconductor devices such that act as an one way switch. When the anode potential is bigger than 0.7 volts relative to the cathode potential, diode will turn on. Threshold voltage of diodes usually is 0.7 volts. A light-emitting diode (LED) is a two-lead semiconductor light source. It is a p–n junction diode, which emits light when activated.

Figure 2: Hot dog and LED

Therefore, when LEDs' pins place along hot dog, those will turn on. When LEDs' pins place vertical relative to hot dog's along, there is not drop potential between pins. So LEDs will turn off. 

Voltage-Divider is a series circuit. Current is common in a series circuit for all of the circuit components. When a resistor is bigger than other resistances in series circuit, its drop voltage is also bigger than other resistances. 

Figure 3: A Voltage Divider Circuit

Figure 4: Current-Divider Circuit

Current-Divider is a parallel circuit. Voltage is common in a parallel 

circuit for all of the circuit components. When a resistor is smaller 

than other resistances in parallel circuit, its current is also bigger than

 other resistances.

Figure 5: Equivalent Resistor



Node Voltage Method

In this method a point of circuit will choose as a reference point of zero voltage. The sum of all currents inter into a node must be equal all of the current that leave node. Current of each branch will calculate according to its voltage divide to its resistance. When equation system solve, nodes voltage will find. Then, current branches will gain.

Figure 6: Node Voltage Method