Capacitors, Magnetic Fields, and Transistors: Electrical Components
Capacitors
Condensers are composed of two metal plates, called armatures, separated by an insulating material called the dielectric. When a voltage is applied, the dielectric prevents current flow, causing charge accumulation on the armatures. Negative charge accumulates on the armature connected to the battery’s negative pole, and positive charge accumulates on the armature connected to the positive pole.
The dielectric becomes polarized due to the accumulated charge. When the voltage is disconnected, the charge is maintained. If the armatures are connected externally, a large current flows, discharging the capacitor to its initial state.
Electric Capacity
The electric capacity is the amount of charge a capacitor can store under a given voltage. Units of capacitance include:
- Microfarad (µF) = 10-6 F
- Nanofarad (nF) = 10-9 F
- Picofarad (pF) = 10-12 F
Capacitor Combinations
- Series: 1/CT = 1/C1 + 1/C2 + 1/C3
- Parallel: CT = C1 + C2 + C3
Capacitors can have a fixed capacity or a variable capacity, where the armature’s position can be adjusted.
Capacity of an Isolated Capacitor
For any capacitor, a relationship exists between charge (q) and potential (V): C = q/V. The capacity depends on the capacitor’s shape and size.
Magnetic Effects of Electric Current
An electric current creates a magnetic field around it. The magnetic field’s direction depends on the current’s direction.
Magnetic Field of a Circular Loop
A current-carrying loop acts like a magnet.
Solenoid
A solenoid is a set of equal, parallel turns carrying the same current. Its magnetic field resembles that of a straight magnet.
Electromagnet
An electromagnet behaves like a magnet when current flows through it. It consists of an iron or steel core (nuclei) with a wire coil wound around it. Each turn of the wire is called a spire. When connected to a DC source, it attracts iron objects due to the magnetic field generated around it.
A solenoid without a core is not an electromagnet. Applications include electric motors, generators, speakers, and locks.
Magnetic Field of a Circular Loop
A current-carrying loop acts like a magnet.
Solenoid
A solenoid is a set of equal, parallel turns carrying the same current. Its magnetic field resembles that of a straight magnet. Inside a solenoid, a magnetic field is visible. Introducing an iron core increases the magnetic field because the solenoid’s magnetism is the sum of the iron’s magnetism.
Light Emitting Diodes (LEDs)
When current passes through an LED, the semiconductor material emits light. Advantages include reduced energy consumption in traffic lights and a lifespan of up to 10 years. A 7-segment display is an alphanumeric indicator that can represent letters and numbers. It is controlled by a programmable electronic circuit. Combining three giant screens with red, green, and blue light allows for generating all other colors. Infrared LEDs are used in remote controls to communicate with TVs using bursts of invisible light.
Transistors
A transistor is an electronic component made of semiconductor material. It has three parts: emitter, base, and collector. There are two types: PNP and NPN. The base is always connected in the middle. The base is the most important element in transistor operation, as small variations in the base current result in significant changes in the emitter current.
Two circuits can be distinguished in a transistor: the control circuit and the utilization circuit. The following relationships hold:
- IE = IC + IB
- IC = IB * β