How Does a Calorimeter Work? Principle, Formula & Key Examples
Brewster’s law describes the specific condition under which light reflected from a surface becomes completely polarized. In the context of Physics and Optics, polarization refers to the orientation of the vibrations of the light wave. Normally, light vibrates in multiple planes as it travels. However, under certain conditions, this vibration can be restricted to just one plane, resulting in polarized light.
When light encounters a transparent medium such as glass or water, part of it is reflected while part enters (refracts) into the new medium. The relationship between the angles of reflected and refracted rays plays a crucial role in understanding polarization through Brewster’s law.
Brewster’s law is important not just for theoretical physics but also for practical applications like glare reduction, photography, and optical instrument design.
Brewster’s Law: Concept and Principle
Brewster’s law states that the maximum polarization of a reflected ray is achieved when the ray strikes the surface at a specific angle known as the Brewster angle. At this special angle, the refracted and reflected rays are exactly perpendicular to each other.
This means the angle between the reflected and the refracted rays is 90 degrees. Under this condition, the reflected light consists entirely of vibrations in a single plane — it is completely polarized.
Polarization by reflection can be observed when light falls on a surface like glass at this critical angle, known as Brewster’s angle.
Brewster’s Law: Formula and Explanation
The mathematical statement of Brewster’s law connects the refractive index of the material and the angle at which polarization occurs.
It is stated as:
| Law / Symbol | Expression / Formula | Description |
|---|---|---|
| Brewster’s Law | tan θB = n | θB: Brewster angle, n: refractive index of medium |
Here, θB is the Brewster angle — the angle of incidence at which reflected light is perfectly polarized. The value of n is the refractive index of the transparent medium (like water or glass) with respect to air.
Step-by-Step Application of Brewster’s Law
- Step 1:
Identify the refractive index (n) for the medium (e.g., n = 1.5 for typical glass).
- Step 2:
Set the formula: tan θB = n.
- Step 3:
Find the Brewster angle: θB = arctan(n).
- Step 4:
The angle θB gives the incidence angle at which reflected light is fully polarized.
- Step 5:
At this angle, the refracted and reflected rays are perpendicular (form a 90° angle).
Example: Calculating Brewster Angle
Let’s apply the formula with a practical example.
Suppose light strikes a glass surface where the refractive index, n, is 1.5.
- Using Brewster’s law:
tan θB = 1.5, so θB = arctan(1.5)
-
Using a calculator, θB ≈ 56.3°
-
Therefore, when light falls at about 56.3° to the normal, the reflected light becomes fully polarized.
Key Points and Applications
- Brewster’s angle is the direction of maximum polarization on reflection.
- At Brewster’s angle, the reflected ray is polarized perpendicular to the plane of incidence — its vibrations lie in a single plane.
- Used in glare reduction in sunglasses, photographic filters, and polarizing devices.
- Understanding Brewster’s law helps in analyzing phenomena involving reflected light, especially in optical instruments and communication technologies.
Summary of Brewster’s Law (Table)
| Feature | Description |
|---|---|
| Condition for Maximum Polarization | Refracted and reflected rays are perpendicular (90° apart) |
| Brewster’s Law Formula | tan θB = n |
| Typical Use Cases | Sunglasses, Photographic lenses, Optical coating design |
| Type of Polarization | Reflected light is linearly polarized |
Related Vedantu Resources and Next Steps
- Thermal Properties of Matter
- Difference Between Heat and Temperature
- Heat Energy and Its Measurement
- Heat Transfer and Thermal Conductivity
- Explore live classes and solved examples on Optics and Light at Vedantu for deeper conceptual clarity.
Summary and Further Learning
Brewster’s law provides a clear, mathematical link between the refractive index of a medium and the angle needed for complete polarization of reflected light. Recognizing and applying this law is vital for mastering optical physics fundamentals and for practical uses in daily life and technology.
Keep practicing angle calculations and observe real-life examples (like the way sunglasses reduce glare) to fully grasp Brewster’s law in action.
FAQs on Calorimeter in Physics: Meaning, Principle & Applications
1. What is a calorimeter?
A calorimeter is a scientific device used to measure the amount of heat exchanged during a physical or chemical process. It usually consists of a well-insulated container to prevent heat loss, ensuring accurate measurement of heat transfer between substances within the system.
2. How does a calorimeter work?
A calorimeter works on the principle of conservation of energy during heat exchange. When two bodies at different temperatures are placed in a calorimeter, heat lost by the hotter body equals the sum of heat gained by the colder body and the calorimeter itself, assuming negligible heat loss to the surroundings.
3. What is the principle of calorimetry?
The principle of calorimetry states that, in an isolated system, heat lost by a hot object is equal to the heat gained by a cold object and the calorimeter. This is based on the law of conservation of energy, which ensures no net heat is lost or gained by the system as a whole.
4. What is the calorimeter constant?
The calorimeter constant (K) is the amount of heat required to raise the temperature of the calorimeter by one degree Celsius. It is expressed as K = (Heat absorbed by calorimeter)/(Rise in temperature). This helps account for the heat absorbed by the calorimeter itself during experiments.
5. Is a calorimeter the same as a thermometer?
No, a calorimeter and a thermometer have different purposes:
- Calorimeter: Measures the amount of heat exchanged between substances.
- Thermometer: Measures the temperature of a substance or system.
While a thermometer may be used inside a calorimeter, the calorimeter as a whole measures energy changes.
6. What are the types of calorimeters?
Common types of calorimeters include:
- Simple (water) calorimeter for basic school and lab experiments
- Bomb calorimeter for measuring heat of combustion or calorific value of fuels
- Coffee cup calorimeter for solution-based reactions at constant pressure
- Adiabatic calorimeter to minimize heat exchange with surroundings, used in advanced studies
7. What is the calorimeter equation?
The calorimeter equation is:
Heat lost by hot substance = Heat gained by cold substance + Heat absorbed by calorimeter.
Mathematically: m1c1(T1−T) = m2c2(T−T2) + K(T−T2)
Where m = mass, c = specific heat, T = temperature, K = calorimeter constant.
8. Why is the calorimeter made of copper?
Copper is commonly used to make calorimeters because:
- It has high thermal conductivity, allowing rapid heat transfer
- It does not easily react with most substances used in experiments
- It is durable and easy to clean, ensuring reliable use over multiple experiments
9. What is water equivalent of a calorimeter?
Water equivalent is the mass of water that would absorb the same amount of heat as the calorimeter for the same temperature increase. It helps simplify calculations, as the calorimeter’s heat absorption can be treated as an equivalent mass of water in energy equations.
10. How do you calculate the final temperature in a calorimeter experiment?
The final temperature (T) is calculated by applying the calorimeter equation and solving for T.
Steps include:
1. Write equations for heat lost and heat gained by the substances and calorimeter.
2. Substitute the values (masses, specific heats, initial temperatures).
3. Set total heat lost = total heat gained.
4. Solve the equation to find the final temperature (T).
11. What is the use of a calorimeter in laboratory experiments?
Calorimeters are used to measure heat changes in various lab processes such as:
- Determining specific heat capacity of solids and liquids
- Measuring enthalpy changes during chemical reactions
- Calculating calorific value of fuels
- Studying phase changes (e.g., melting, fusion, evaporation)
12. How do you determine the calorimeter constant experimentally?
To determine the calorimeter constant (K) experimentally:
1. Add a known quantity of hot water to a known quantity of cold water in the calorimeter.
2. Record the initial temperatures and final equilibrium temperature.
3. Calculate heat lost and gained.
4. Use the formula K = (Heat lost by hot - Heat gained by cold) / (Rise in temperature of calorimeter) to find the calorimeter constant.
