Introduction to Physics

Pressure

It is the force exerted per unit area on a surface (F/A). It is a measure of how concentrated a force is over a given area.

Analogy (Punching vs Stabbing)

Punching: Lower pressure due to a larger surface area → effective for delivering force, but may not penetrate or cause significant damage.
Stabbing: Higher pressure due to a smaller surface area → more effective at penetrating and damaging the target

High Pressure to Low Pressure

Fluids (liquids and gases) naturally flow from areas of high pressure to areas of low pressure. This movement occurs because fluids seek to equalize pressure differences within a system.

Ex. Drinking Straw

Atmospheric pressure is the force exerted by air molecules colliding with surfaces, including the inside of the straw.
When you suck on the straw, you decrease the volume of air at the top of the straw, which lowers the number of air molecules present in that space.
This reduction in the number of air molecules leads to a decrease in pressure
When the pressure inside the straw (Pinside) becomes lower than the atmospheric pressure (Patmospheric) outside the straw, the pressure difference creates a net force.

Current (I) ↔ Force (F): More current means more flow, just like more force means more movement.
Voltage (V) ↔ Pressure (P): Higher voltage creates a stronger push for the current, similar to how higher pressure pushes more fluid through a system.

Current (amperes (A))

Current is the flow of electric charge through a conductor, such as a wire. It is what powers electrical devices, allowing energy to move from one place to another.
1 ampere means that one coulomb of charge

Types of Current:

Direct Current (DC): Current flows in one direction. Batteries provide DC power.

Alternating Current (AC):
It is a type of current changes direction periodically. This is the type of electricity supplied to homes and businesses.
For example, in standard household AC, the current changes direction 60 times per second in the U.S. (60 Hz) or 50 times per second in many other countries (50 Hz).

AC voltage can be easily transformed using transformers, allowing it to be stepped up for long-distance transmission and then stepped down for use in homes and businesses.

Voltage (volts (V))

Voltage is defined as the amount of work needed to move a unit of electric charge from one point to another.

Phase

It is the position of a point in time on an alternating current (AC) waveform

Single-Phase: In a single-phase system, there is only one waveform or cycle of alternating current (AC). The current flows in one direction, then reverses, creating a single alternating current wave.

Three-Phase: In a three-phase system, there are three separate AC waveforms. These waves are spaced 120 degrees apart, meaning the peak of each wave occurs at different times. This provides more consistent and balanced power.

Phase Shift

It is the difference in position between two AC waveforms. For example, in a single-phase motor, the capacitor creates a phase shift between the start winding and run winding, allowing the motor to create a rotating magnetic field.

Phase Angle

It is measured in degrees (0° to 360°) and indicates how far one waveform is ahead or behind another.

Power

It is the amount of work done or energy transferred per unit of time. The higher the number of watts, the greater the energy being transferred per second.
P = V × I

What happens when I connect my charger to the power outlet?

Charger converts 240V AC from power outlet to 5V DC for the phone.
The charger is rated for 15W output at 5V. So it requires 3mA
The charger needs to draw more power from the 240V AC to produce the 15W DC output. Since it's a step-down transformer, we can calculate how much current is drawn from the 240V AC side.
The charger is not 100% efficient (in reality, some power is lost as heat), but assuming it's around 85% efficient, we can use the following relation:

Battery Capacity

It is the amount of charge a battery can deliver over time. Specifically, it tells you how much current a battery can supply over a given period before it is fully discharged.
Ex. My phone's battery capacity is 5000mAh
1 mAh = 1 milliamps (mA) of current flowing for 1 hour

Transformer

It is a device that transfers electric energy from one alternating-current circuit to one or more other circuits, either increasing (stepping up) or reducing (stepping down) the voltage.

The transformer works on the basic principles of electromagnetic induction and mutual induction.

Types of Transformer

Power Transformer

It is used in the transmission network for stepping up or stepping down the voltage at high power levels.

Distribution Transformer

It steps down the voltage for distribution to end-users like residential, commercial, or small industrial applications

Instrument

Tachometer

It is a device used to measure the rotational speed of an object, typically a shaft or a disk in a motor or other machinery. It provides readings in revolutions per minute (RPM) or other angular velocity units. Tachometers are widely used in automobiles, industrial machines, and various mechanical systems.

Multimeter

It is an essential electronic measuring tool used by professionals and hobbyists to measure and diagnose electrical parameters such as voltage, current, resistance, and other circuit characteristics. It combines the functions of a voltmeter, ammeter, and ohmmeter into one device.

It measures DC voltage (batteries, circuits) and AC voltage (mains power).
It measures DC and AC currents.
It measures resistance in a circuit or component.
It tests if a circuit is complete by giving a beep or light indicates continuity.

Magnetron

It is a versatile electronic measuring instrument used to measure electrical parameters such as voltage, current, and resistance. It combines the functions of a voltmeter, ammeter, and ohmmeter into a single device. Modern multimeters can also measure additional parameters like capacitance, frequency, continuity, and temperature.