Physics with Sir Mehboob Mughal

Key points
Chapter 06
Static fluid
For MDCAT preparation

The photoelectric effect is the phenomenon in which light ejects electrons from the surface of a metal.

When light shines on a metal surface, the energy of the light can be absorbed by the electrons in the metal.
If the light has enough energy, the electrons get knocked out of the metal.
These ejected electrons are called photoelectrons.

🔑 Key Points to Remember

1️⃣ Light behaves like particles (photons)

Light is made of tiny packets of energy called photons.

Each photon has energy:

E = h f

= Planck’s constant

= frequency of light

2️⃣ Threshold Frequency ()

There is a minimum frequency needed to eject electrons.

If frequency < , no electrons are released, no matter how bright the light is.

3️⃣ Kinetic Energy of Ejected Electrons

Einstein gave the equation:

K.E = h f - hf°

= work function (minimum energy needed to remove an electron)

4️⃣ Intensity Matters Differently

Increasing frequency increases the energy of electrons.

Increasing intensity (brightness) increases the number of electrons, not their energy.

🌞 Real-Life Examples

Solar panels work due to the photoelectric effect.

Automatic doors use photoelectric sensors.

Light meters in cameras.

---

🎯 Why It Is Important?

The photoelectric effect proved that light has particle nature, which helped start quantum physics

General theory of relativity

Triple point:
Triple Point is a unique temperature and pressure at which a substance can exist simultaneously in all three states of matter — solid, liquid, and gas — in thermodynamic equilibrium.

Definition:

> The triple point of a substance is the specific condition of temperature and pressure where solid, liquid, and v***r phases coexist in equilibrium.

Example (Water):

For pure water, the triple point occurs at:

Temperature: 0.01°C (273.16 K)

Pressure: 611.657 Pa (≈ 0.00604 atm)

At this point:

Ice, liquid water, and water v***r coexist together.

Importance:

1. Fundamental reference point — used to define the Kelvin temperature scale.

2. Used for calibration of thermometers.

3. Helps in studying phase diagrams and state changes of substances.

In a Phase Diagram:

At the triple point, the solid–liquid, solid–gas, and liquid–gas equilibrium lines intersect.

June 14, 2023 Projectile Motion:When a body is thrown in the air with its initial velocity at an angle along horizontally, it follows subsequently parabolic curve path und...