9.4 Practical circuits

• A dimmer is a device used to vary the brightness of an electric light by changing the voltage supplied to it.
• A fixed resistor is an electrical component with a set resistance value that cannot be adjusted.
• A variable resistor, also known as a potentiometer or rheostat, is an electrical component whose resistance can be adjusted manually or electronically to control the flow of electric current.
• Volume refers to the perceived loudness or intensity of sound, typically controlled by adjusting the amplitude of an audio signal.
• Variable resistors are essential components in circuits where resistance needs to be adjusted, such as in dimmer switches for lamps or volume controls in music players. They allow users to change the resistance according to their preference. In dimmer switches, variable resistors control the brightness of lamps by adjusting the resistance in the circuit.
• Similarly, in audio equipment, sliding controls serve as variable resistors for adjusting volume. The symbol for a variable resistor resembles that of a fixed resistor but includes an arrow. By increasing the resistance of the variable resistor, the current in the circuit decreases, dimming the lamp, while decreasing the resistance increases the current, making the lamp brighter.
• Electric circuits are ubiquitous in everyday life, found in various devices like refrigerators, cars, and battery-operated equipment. For instance, when a refrigerator door is opened, a circuit activates the interior light. Similarly, warning buzzers in cars can be adjusted for loudness and are triggered when certain conditions are met, such as opening the door while the headlamps are on.
• In vehicles powered by 12 V batteries, battery voltage indicators help monitor battery levels. These indicators are connected to the battery through a parallel circuit with a switch, allowing voltage measurement when needed.
• Moreover, circuits may adapt different voltage requirements using resistors. For example, a 6 V lamp can be safely operated with a 12 V battery by using resistors to distribute voltage evenly. This ensures the lamp receives the correct voltage and functions properly.
• When opening the door of a refrigerator (fridge), a light comes on

  inside. The circuit for this is shown in the diagram.

  The switch is opened and closed by the movement of the fridge door.

  When the door is open, the switch is closed and when the door is closed, the switch is open.
• Some equipment is fitted with a buzzer to make a warning sound if

  something is done incorrectly. Often, the loudness of the sound can be

  adjusted. This circuit shows how this is done. Some cars have a buzzer that makes a sound when the driver opens the door while the headlamps are switched on. The door of the car controls the switch for the buzzer, but the buzzer should only operate when the

  headlamps are on.
• Practical Circuits

  
• Practical Circuits: