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PARAMOUNT SCHOOL SYSTEM

Subject: Physics – I

Unit 7: Density and Temperature

QI. Choose the best possible option.

How many phases of matter are there?

A. 1 B. 2 C. 3 D. 4
In which of the materials, particles have only vibrational motion?

A. Solids B. Liquids C. Gas D. Plasma
Which amount of water has greater density at room temperature?

A. 100 g B. 1 kg C. 1 ton D. All have same density
What is the mass of a liquid of density 50 kg m⁻³ in a container of volume 5 m³?

A. 200 kg B. 225 kg C. 250 kg D. 275 kg
Gases and liquids are categorized as:

A. Liquids B. Gases C. Fluids D. Solids
Which statement describes the particle structure of gases?

A. Particles are tightly packed and have strong bonds.

B. Particles have moderate kinetic energy and move randomly.

C. Particles are arranged in a repeating pattern.

D. Particles have fixed positions and low kinetic energy.
Which state of matter has particles that are highly compressible and can fill any container?

A. Solid B. Liquid C. Gas D. Plasma
What happens to the arrangement of particles when a solid is heated and turns into a liquid?

A. Particles become more closely packed.

B. Particles move farther apart.

C. Particles start vibrating in fixed positions.

D. Particles change their state from solid to gas.
Which of the following is NOT a form of internal energy?

A. Kinetic energy of the particles B. Potential energy of the particles

C. Chemical energy of the bonds between the particles D. Light energy
When an ideal gas is expanded keeping its temperature constant, its internal energy:

A. Increases B. Decreases C. Remains the same D. Cannot be determined
Which of the following physical properties is used in a mercury thermometer?

A. Electrical resistance B. Pressure C. Volume D. Colour
Which of the following can increase the sensitivity of a liquid-in-glass thermometer?

A. Use a bigger bulb which contains more liquid

B. Use a longer capillary tube

C. Using liquid with a high specific heat capacity

D. Changes colour on temperature
Which thermometer is most suitable for measuring rapidly changing temperatures?

A. Constant volume gas thermometer B. Resistance thermometer

C. Liquid in glass thermometer D. Thermocouple
Mercury has uniform linear expansion in liquid-in-glass thermometers. A liquid-in-glass thermometer has a mercury level of 2 cm at the melting point of ice and 6 cm at the boiling point of water. What is the distance between every 1°C division on the Celsius scale of the thermometer?

A. 0.04 cm B. 0.06 cm C. 0.08 cm D. 1.00 cm
Which thermometer uses voltage to measure the temperature of a hot body?

A. Thermocouple B. Resistance thermometer

C. Liquid in glass thermometer D. Gas thermometer

SHORT RESPONSE QUESTIONS

QII. Give a short response to the following questions

1. Two liquids A and B, have densities 1 g/mL and 1.2 g/ml, respectively. When both liquids are poured into a container, one liquid floats on top of the other. Which liquid is on top, and why?

When two liquids with different densities are poured into the same container, the liquid with the lower density will float on top of the liquid.

In this case:

Liquid A has a density of 1 g/mL.
Liquid B has a density of 1.2 g/mL.

Since liquid A is less dense than liquid B, liquid A will float on top of liquid B.

2. Write a method to find the volume and density of a human body?

To find the volume and density of a human body, we use a displacement method. We will follow these steps:

Measure Mass: Use a weighing scale to find the mass of the person (in kilograms).

Water Displacement:

Fill a large container (like a tank) with water and note the initial water level (Vᵢ).
Fully submerge the person in the water without touching the sides or bottom of the container.
Measure the new water level (V_f) after submersion.

Calculate Volume:

The volume of the human body is the difference between the final and initial water levels.
Volume (m³) = V_f– Vᵢ.

Calculate Density:

Use the formula.
Express the density in kg/m³.

This method provides the body volume and density by using the water displacement technique.

3. How is plasma the fourth state of matter? Give a reason

Plasma is the fourth state of matter formed when a gas is heated to very high temperatures, causing atoms to ionize into positive ions and free electrons. This ionized gas conducts electricity and reacts to magnetic fields, making it different from solids, liquids, and gases. Plasma is found in the Sun, stars, and neon lights.

4. Why water is not used in liquid in glass thermometers?

Water is not used in liquid-in-glass thermometers because it has a high freezing point (0°C) and a low boiling point (100°C), which limits its temperature range. Additionally, water does not expand uniformly with temperature changes, making it unsuitable for accurate temperature measurements.

5. Can we increase internal energy of a substance without increasing its temperature?

Yes, we can increase the internal energy of a substance without increasing its temperature by changing its state, such as melting ice into water or evaporating water into steam. During these phase changes, energy is absorbed to break molecular bonds, but the temperature remains constant.

6. Why are fixed point scales required for thermometers? What difficulties are there when setting fixed points for thermometer scales?

Fixed point scales are required for thermometers to ensure accurate and consistent temperature measurements. They use standard reference points, like the melting point of ice (0°C) and the boiling point of water (100°C), to calibrate the thermometer.

Difficulties in setting fixed points include the need for pure substances, controlling pressure (since boiling points change with pressure), maintaining stable conditions, ensuring linearity of the thermometer, and accessibility to reference points under different conditions.

7. Mercury is replaced with alcohol in liquid in glass thermometers. Discuss the possible change in sensitivity and range of thermometer?

Replacing mercury with alcohol increases the sensitivity of the thermometer since alcohol expands more for small temperature changes. However, it decreases the range because alcohol has a lower boiling point, limiting its use at high temperatures but allowing it to measure much lower temperatures than mercury.

8. Why -273.15°C temperature is called absolute zero? Can we achieve this temperature?

The temperature of -273.15°C is called absolute zero because it is the lowest possible temperature where the motion of particles theoretically stops, meaning they have zero kinetic energy. We cannot achieve this temperature in practice, as it is impossible to completely stop all particle motion.

9. Why thermocouple thermometer is suitable to measure high temperatures but not liquid in glass thermometer? Why is a thermocouple thermometer good for measuring high temperatures but a liquid in glass thermometer is not?

A thermocouple thermometer is suitable for measuring high temperatures because it uses two different metals to generate an electric voltage that changes with temperature. This design can withstand very high temperatures without getting damaged. In contrast, a liquid-in-glass thermometer uses mercury or alcohol, which can evaporate or break down at high temperatures, making it unsuitable for such conditions.

10. Can we increase the sensitivity of a liquid-in-glass thermometer without changing its range?

Yes, we can increase the sensitivity of a liquid-in-glass thermometer by using a thinner capillary tube or a larger bulb, which allows the liquid to rise more for small temperature changes, without changing its overall range.

11. One student claims to have constructed a more sensitive liquid in glass thermometer. How can her claim be verified?

The student’s claim can be verified by comparing her thermometer with a standard thermometer. To do this, the temperature should be measured at different known temperatures, and if her thermometer shows smaller changes (more sensitivity) for the same temperature difference, the claim can be confirmed.

LONG RESPONSE QUESTIONS

QIII. Give an extended response to the following

1. Define density. Describe methods to determine densities of regular and irregular-shaped solids, liquids and gases.

Density:

Density is the mass of a substance per unit volume.

Formula:

Unit:

The unit of density is kilograms per cubic meter (kg/m³) or grams per cubic centimeter (g/cm³).

Quantity:

Density is a scalar quantity.

Methods to Determine Density:

1. Regular-shaped Solids:

Step 1: Measure the mass using a balance.
Step 2: Calculate the volume using the formula for the shape (e.g., volume of a cube = side³).
Step 3: Use the density formula to find the density.

2. Irregular-shaped Solids (Displacement Method):

Step 1: Measure the mass using a balance.
Step 2: Fill a measuring cylinder with water and record the initial volume V_i.
Step 3: Submerge the object in water and record the new volume V_f.
Step 4: Subtract the initial volume from the final volume to get the volume of the object.
Step 5: Use the density formula.

3. Liquids

Step 1: Weigh an empty measuring cylinder.
Step 2: Add liquid and measure the total mass.
Step 3: Subtract the mass of the empty cylinder to find the mass of the liquid.
Step 4: Read the volume of the liquid from the measuring cylinder.
Step 5: Use the density formula.

4. Gases

Step 1: Capture a known volume of gas in a sealed container.
Step 2: Measure the mass of the container with and without gas.
Step 3: Subtract to find the mass of the gas.
Step 4: Use the known volume of the container and apply the density formula.

2. How would you distinguish between solids, liquids and gases on the basis of attractive forces between particles and the motion of particles?

Solids	Liquids	Gases
Very strong attractive forces; particles tightly packed	Moderate attractive forces; particles can move slightly	Very weak attractive forces; particles far apart
Closely packed in a regular pattern	Particles are close but not in a fixed pattern	Randomly arranged with large spaces
Particles vibrate around fixed positions	Particles slide past each other	Particles move freely and rapidly in all directions
Low energy	Moderate energy	High energy
Definite shape and volume	Takes shape of container, fixed volume	No definite shape or volume, expands to fill container
High density	Medium density	Low density
Examples: Ice, iron	Examples: Water, oil	Examples: Air, helium

3. Describe two different physical properties that vary with temperature and explain how these properties can be used to measure temperature.

Two physical properties that vary with temperature and can be used to measure temperature are volume expansion of liquids and pressure change in gases.

Volume Expansion of Liquids:

Most liquids expand when heated. This is the principle used in mercury and alcohol thermometers. As the temperature of the liquid increases, its volume expands in a uniform way. For example, in a liquid-in-glass thermometer, the mercury expands as it absorbs heat, and the position of the mercury indicates the temperature. The greater the temperature, the further the mercury rises in the tube, providing a reading on the temperature scale.

Pressure Change in Gases:

The pressure of a gas increases as its temperature rises, provided the volume is kept constant. This principle is used in constant volume gas thermometers. In such thermometers, as the gas in the bulb is heated, its particles move faster and collide more frequently with the walls of the container, which increases the pressure. The pressure change is then used to determine the temperature. This relationship is governed by Gay-Lussac’s law, which states that the pressure of a gas is directly proportional to its temperature when the volume is constant.

Both these properties can be accurately measured and used for temperature sensing, as they show a predictable and consistent change with temperature variations.

4. Describe the construction and working of different types of gas thermometers.

Gas thermometers operate based on the relationship between the temperature of a gas and its volume or pressure, as described by the gas laws. There are different types of gas thermometers, each with specific construction and working principles:

Constant Pressure Gas Thermometer:

Construction:

This type consists of a glass tube filled with a gas (usually helium or hydrogen) connected to a reservoir where the gas is kept at a constant pressure. The gas is contained within the tube, which is often equipped with a scale to measure its volume.

Working:

The thermometer works by observing the change in volume of the gas as the temperature changes. According to Charles’ Law (for constant pressure), the volume of a gas is directly proportional to its temperature. As the temperature increases, the gas expands, and this expansion is measured as a change in volume, which is then correlated to temperature.

Constant Volume Gas Thermometer:

Construction:

This thermometer consists of a sealed container with a fixed volume of gas. The container is usually connected to a manometer or pressure gauge to measure the pressure of the gas inside.

Working:

In a constant volume gas thermometer, the temperature is determined by the change in pressure of the gas, as per Gay-Lussac’s Law, which states that the pressure of a gas at constant volume is directly proportional to its absolute temperature. As the temperature increases, the pressure of the gas rises, and this pressure change is used to measure the temperature.

5. Analyze how the structure of a liquid-in-glass thermometer can be modified to improve its performance. Give a detailed answer.

To improve the performance of a liquid-in-glass thermometer, the following structural modifications can be made:

1. Diameter of the Capillary Tube:

A thermometer with a smaller diameter capillary tube can detect smaller temperature changes because it allows a smaller volume of liquid, which reacts more quickly to absorbed heat and rises more rapidly.

2. Nature of the Liquid:

Using liquids like mercury or alcohol, which expand more than other liquids like water, can increase the sensitivity of the thermometer. These liquids respond more significantly to temperature changes.

3. Size of the Bulb:

A larger bulb contains more liquid, which can expand more, allowing the thermometer to cover a larger temperature range.

4. Nature of the Glass:

The type of glass used impacts the linearity of the thermometer. Using borosilicate glass, which has a more linear expansion coefficient, can improve the thermometer’s linearity, ensuring that temperature changes are represented more consistently on the scale.