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The following tables show some of the more commonn symbols used for representing the electronics components in circuit diagrams.

Resistor Symbols

Symbol Function
A resistor restricts the flow of current, for example to limit the current passing through an LED. A resistor is used with a capacitor in a timing circuit.
This type of variable resistor with 2 contacts (a rheostat) is usually used to control current. Examples include: adjusting lamp brightness, adjusting motor speed, and adjusting the rate of flow of charge into a capacitor in a timing circuit.
This type of variable resistor with 3 contacts (a potentiometer) is usually used to control voltage. It can be used like this as a transducer converting position (angle of the control spindle) to an electrical signal

Capacitor Symbols

Symbol Function
A capacitor stores electric charge. A capacitor is used with a resistor in a timing circuit. It can also be used as a filter, to block DC signals but pass AC signals.
A capacitor stores electric charge. This type must be connected the correct way round. A capacitor is used with a resistor in a timing circuit. It can also be used as a filter, to block DC signals but pass AC signals.
A variable capacitor is a capacitor whose capacitance may be intentionally and repeatedly changed mechanically or electronically. Variable capacitors are often used in L/C circuits to set the resonance frequency, e.g. to tune a radio (therefore they are sometimes called tuning capacitors), or as a variable reactance, e.g. for impedance matching in antenna tuners.

Diode Symbols

Symbol Function
A diode is a two-terminal electronic component with asymmetric conductance, it has low (ideally zero) resistance to current flow in one direction, and high (ideally infinite) resistance in the other.
A Zener diode is a diode which allows current to flow in the forward direction in the same manner as an ideal diode, but also permits it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, "zener knee voltage", "zener voltage", "avalanche point", or "peak inverse voltage".
A tunnel diode or Esaki diode is a type of semiconductor that is capable of very fast operation, well into the microwave frequency region, made possible by the use of the quantum mechanical effect called tunneling. They have negative differential resistance in part of their operating range, and therefore are also used as oscillators, amplifiers, and in switching circuits using hysteresis.
A light-emitting diode (LED) is a two-lead semiconductor light source that resembles a basic pn-junction diode, except that a LED also emits light. When an LEDs anode lead has a voltage that is more positive than its cathode lead by approximately 0.6 to 2.2 Volts, current often flows and light is often emitted. On the other hand, when an LEDs anode lead has a voltage that is less positive than its cathode lead by approximately 0.6 to 2.2 Volts, current often does not flow and light is often not emitted.
A photodiode is a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation. If the anode and cathode leads of a photodiode are joined together by a wire, when in the dark, no current will flow. On the other hand, when in the light, current flows from the cathode to the anode.
A varicap diode, varactor diode, variable capacitance diode, variable reactance diode or tuning diode is a type of diode whose capacitance varies as a function of the voltage applied across its terminals.
The Schottky diode, also known as hot carrier diode is a semiconductor diode with a low forward voltage drop and a very fast switching action.

Transistor Symbols

Symbol Function
NPN is one of the two types of bipolar transistors, consisting of a layer of P-doped semiconductor (the "base") between two N-doped layers. A small current entering the base is amplified to produce a large collector and emitter current. That is, when there is a positive potential difference measured from the emitter of an NPN transistor to its base (i.e., when the base is high relative to the emitter) as well as positive potential difference measured from the base to the collector, the transistor becomes active. In this "on" state, current flows between the collector and emitter of the transistor. Most of the current is carried by electrons moving from emitter to collector as minority carriers in the P-type base region. To allow for greater current and faster operation, most bipolar transistors used today are NPN because electron mobility is higher than hole mobility.
The other type of BJT is the PNP, consisting of a layer of N-doped semiconductor between two layers of P-doped material. A small current leaving the base is amplified in the collector output. That is, a PNP transistor is "on" when its base is pulled low relative to the emitter. The arrows in the NPN and PNP transistor symbols are on the emitter legs and point in the direction of the conventional current flow when the device is in forward active mode. A mnemonic device for the PNP transistor symbol is "pointing in (proudly/permanently)," based on the arrows in the symbol and the letters in the name.
In a junction field-effect transistor, or JFET, the controlled current passes from source to drain, or from drain to source as the case may be. The controlling voltage is applied between the gate and source. Note how the current does not have to cross through a PN junction on its way between source and drain: the path (called a channel) is an uninterrupted block of semiconductor material. In the image just shown, this channel is an N-type semiconductor.
A P-Channel JFET is a JFET whose channel is composed primarily of holes as the charge carrier. This means that when the transistor is turned on, it is primarily the movement of holes which constitutes the current flow. This is in contrast to N-Channel JFETs, whose channel is composed primarily of electrons, which constitute the current flow. A P-Channel JFET is composed of a gate, a source and a drain terminal.
The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a transistor used for amplifying or switching electronic signals. Although the MOSFET is a four-terminal device with source (S), gate (G), drain (D), and body (B) terminals, the body (or substrate) of the MOSFET often is connected to the source terminal, making it a three-terminal device like other field-effect transistors. Because these two terminals are normally connected to each other (short-circuited) internally, only three terminals appear in electrical diagrams. The MOSFET is by far the most common transistor in both digital and analog circuits, though the bipolar junction transistor was at one time much more common.

Coil Symbols

Symbol Function
An inductor, also called a coil or reactor, is a passive two-terminal electrical component which resists changes in electric current passing through it. It consists of a conductor such as a wire, usually wound into a coil. When a current flows through it, energy is stored temporarily in a magnetic field in the coil. When the current flowing through an inductor changes, the time-varying magnetic field induces a voltage in the conductor, according to Faraday’s law of electromagnetic induction, which opposes the change in current that created it.