This is a parallel circuit that has a 1.5 volt battery and 2 1.5 volt LEDs and it works half the time
Here there is a 9 volt battery and a 1.5 volt LED and since 9 volts is greater than 1.5 volts the LED explodes
This is a circuit in series with two leds of 1.5 V and two batteries of 1.5 V
This is a circuit with one battery of 1.5 V and one led of 1.5 V
In electrical engineering, circuit theory is that which includes the fundamentals for the analysis of electrical circuits and allows the determination of the voltage and current levels at each point of the circuit in response to a certain excitation.
Here you have a video.
En ingeniería eléctrica, la teoría de circuitos es aquella que comprende los fundamentos para el análisis de circuitos eléctricos y permite determinar los niveles de tensión y corriente en cada punto del circuito en respuesta a una determinada excitación.
Aqui teneis un video.