Quiz Class 9th Science 14-05-2026

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Q1. Which substance undergoes sublimation?

Correct Answer: Camphor (Kapoor)

Description

Sublimation is a special physical process in which a solid substance changes directly into gas without changing into liquid first. Camphor is one of the best and most common examples of sublimation. When camphor is kept in an open place, it slowly becomes smaller and finally disappears because its particles directly mix into the air as vapour.

This happens because the particles of camphor are weakly attached. When they get heat energy from surroundings, they move faster and escape into the air. No liquid form is seen during this process.

Sublimation is important in science because it helps us understand how particles behave in different states of matter.

Step-by-Step Process

1. Camphor starts in solid form.
2. Heat from surroundings reaches the solid.
3. The particles gain energy and start vibrating faster.
4. The particles break away from the solid surface.
5. They directly change into gas particles.
6. The vapour spreads into the air.

Detailed Example

Suppose you keep a few camphor tablets in a room for several days.

• On the first day, the tablets are clearly visible.
• Slowly, the tablets become smaller.
• After some time, they completely disappear.
• No liquid is found around them.

This proves that camphor changed directly from solid into gas.

Another example is naphthalene balls used in cupboards. They also slowly disappear because of sublimation.

Key Points

• Sublimation = Solid directly changes into gas
• No liquid stage appears
• Camphor is a sublimating substance
• It is a physical change
• Used in medicines and air fresheners

Q2. SI unit of work is:

Correct Answer: Joule

Description

In Physics, work is said to be done when a force moves an object through a certain distance. The SI unit of work is Joule (J).

For example:

• Lifting a school bag
• Pushing a table
• Pulling a cart

All these activities involve work because force causes movement.

If force is applied but the object does not move, then no work is done.

Formula of Work

Work = Force × Distance

W = F × d

Where:

• W = Work
• F = Force
• d = Distance

How This Formula Came

Scientists observed that work depends mainly on two things:

1. How much force is applied
2. How far the object moves

If either force or distance increases, work also increases.

Understanding with Simple Logic

• More force = More work
• More distance = More work

So both values are multiplied.

That is why:

Work = Force × Distance

Step-by-Step Process

1. Apply force on an object.
2. The object starts moving.
3. Measure the distance travelled.
4. Measure the amount of force used.
5. Multiply force and distance.
6. The result is called work.

Detailed Example

Suppose a boy pushes a box with a force of 10 Newton and the box moves 5 metres.

Step 1: Write Formula

Work = Force × Distance

Step 2: Put Values

Work = 10 × 5

Step 3: Multiply

Work = 50 Joules

So, the work done is 50 J.

Real-Life Examples

• Carrying a water bucket upstairs
• Kicking a football
• Lifting books onto a shelf
• Pulling luggage at a railway station

Key Points

• SI unit of work = Joule
• Symbol = J
• Work depends on force and movement
• No movement means no work
• Formula: W = F × d

Q3. Atomic mass is the sum of:

Correct Answer: Protons and Neutrons

Description

Atomic mass is the total mass present inside the nucleus of an atom. It is calculated by adding the number of protons and neutrons.

Atoms are made of three basic particles:

• Protons
• Neutrons
• Electrons

Protons and neutrons are found inside the nucleus. Electrons move around the nucleus.

Electrons are not included in atomic mass because their mass is extremely small compared to protons and neutrons.

How This Formula Came

Scientists discovered that almost the entire mass of an atom is concentrated inside the nucleus.

Since:

• Proton has mass
• Neutron has mass
• Electron mass is very small

Therefore:

Atomic Mass = Protons + Neutrons

Step-by-Step Process

1. Find the number of protons.
2. Find the number of neutrons.
3. Add both numbers together.
4. The total gives atomic mass.

Detailed Example

Carbon atom contains:

• 6 protons
• 6 neutrons

Step 1:

Atomic Mass = Protons + Neutrons

Step 2:

Atomic Mass = 6 + 6

Step 3:

Atomic Mass = 12

So, the atomic mass of carbon is 12 amu.

Real-Life Importance

Atomic mass helps scientists:

• Identify elements
• Study chemical reactions
• Make medicines
• Understand atomic structure

Key Points

• Atomic mass = Protons + Neutrons
• Measured in amu
• Electrons are ignored
• Nucleus contains most mass

Q4. Distance is a:

Correct Answer: Scalar Quantity

Description

Distance is called a scalar quantity because it only has magnitude and no direction.

It tells the total path travelled by an object.

For example:
If a student walks around a playground and returns to the starting point, the total path covered is distance.

Direction is not important in distance.

Difference Between Scalar and Vector

Scalar Quantity

• Has only magnitude
• No direction

Examples:

• Distance
• Speed
• Mass

Vector Quantity

• Has magnitude and direction

Examples:

• Velocity
• Force
• Displacement

Why Distance is Scalar

Distance only answers:
“How much path is covered?”

It does not answer:
“In which direction?”

Therefore, distance is scalar.

Step-by-Step Process

1. Observe movement of object.
2. Measure total path covered.
3. Ignore direction.
4. Final value is distance.

Detailed Example

A boy walks:

• 5 metres east
• then 5 metres west

Total Distance

5 + 5 = 10 metres

Even though he returned to starting point, distance is still 10 metres because total path is counted.

Real-Life Examples

• Distance from school to home
• Length of a road
• Distance travelled by a bus

Key Points

• Distance is scalar
• Only magnitude matters
• Direction is not needed
• SI unit = metre

Q5. Epithelial tissue is responsible for:

Correct Answer: Protection

Description

Epithelial tissue forms the protective covering of the body. It covers:

• Skin
• Internal organs
• Blood vessels
• Digestive organs

The cells are tightly packed together and form a protective layer. This layer protects the body from:

• Dust
• Germs
• Injury
• Water loss

Epithelial tissue acts like a shield around body parts.

How Protection Happens

1. Cells remain closely packed.
2. They form continuous sheets.
3. Harmful substances cannot easily enter.
4. Internal organs stay safe.

Step-by-Step Process

1. Epithelial cells join together.
2. They form outer covering layers.
3. The covering protects body parts.
4. Germs and dust are blocked.
5. Body remains protected from damage.

Detailed Example

Human Skin

The outer layer of skin is made of epithelial tissue.

Functions:

• Protects from germs
• Prevents water loss
• Protects from sunlight and injury

Stomach Lining

The stomach contains acids for digestion. Epithelial tissue protects stomach walls from these acids.

Types of Epithelial Tissue

• Squamous epithelium
• Cuboidal epithelium
• Columnar epithelium
• Ciliated epithelium

Each type performs special protective functions.

Key Points

• Main function = Protection
• Covers body surfaces
• Cells are tightly packed
• Prevents infection and injury
• Found in skin and organs

Quick Revision Notes

Sublimation

• Solid directly changes into gas
• Example: Camphor

Work

• Formula: Force × Distance
• SI unit: Joule

Atomic Mass

• Protons + Neutrons

Distance

• Scalar quantity
• No direction

Epithelial Tissue

• Protects body organs