Question

For a class demonstration, your physics instructor uniformly heats a bimetallic strip that is held in a horizontal orientation. As a result, the bimetallic strip bends upward. This tells you that the coefficient of linear thermal expansion for metal \(\mathrm{T}\), on the top is_____that of metal \(\mathrm{B}\), on the bottom. a) smaller than b) larger than c) equal to

Short answer

Answer: The coefficient of linear thermal expansion for the top metal (T) is larger than that of the bottom metal (B).

Step-by-step solution

Understand the concept of a bimetallic strip

A bimetallic strip consists of two different metals which are bonded together. When heated, the two metals expand at different rates, causing the strip to bend. In this case, the strip bends upwards, meaning that the top metal (T) either expands more or contracts less than the bottom metal (B).

Define the coefficient of linear thermal expansion

The coefficient of linear thermal expansion (denoted as \(\alpha\)) is a measure of the change in length or size of a material when it is heated or cooled. A higher value of \(\alpha\) means that the material expands more when heated. Since the strip bends upwards, it indicates that the top metal (T) expands more than the bottom metal (B).

Determine the relationship between \(\alpha_T\) and \(\alpha_B\)

According to the given information, the bimetallic strip bends upwards when heated. This implies that the top metal (T) expands more than the bottom metal (B). Thus, the coefficient of linear thermal expansion for metal T is larger than that of metal B.

Select the correct option

Based on the relationship determined in Step 3, we can conclude that the answer is: b) larger than

Key concepts

Bimetallic Strip

Bimetallic strips are ingeniously simple devices made of two different metals bonded together. They are foundational in various applications because of their ability to convert temperature changes into mechanical displacement. How does it work? Each metal in the strip has its distinct coefficient of linear thermal expansion. When the temperature changes, each metal expands or contracts at its rate, causing the strip to bend. This is due to the differential expansion rate of the metals.

For students, observing a bimetallic strip in action can dramatically improve understanding of physical properties of materials and thermodynamics. For instance, if you see a bimetallic strip bending upwards upon heating, as in the textbook exercise, it means the metal on the top is expanding more than the one at the bottom. This expansion indicates a difference in the properties, specifically, the coefficient of linear thermal expansion between the metals.

• Bimetallic strips are used in various devices, from thermostats to fire alarms.
• Understanding their working principle enhances comprehension of concepts like material science and thermodynamics.
• The behavior of these strips is a visually effective demonstration of thermal expansion in different materials.

Thermal Expansion

Understanding thermal expansion is crucial in physics education and numerous practical applications. It refers to the tendency of matter to change in volume in response to a change in temperature. When materials are heated, their particles move faster and tend to take up more space, causing the materials to expand. The coefficient of linear thermal expansion, denoted by \(\alpha\), quantifies how much a material lengthens per degree change in temperature.

In the context of the bimetallic strip, the metal with the higher coefficient of linear thermal expansion will expand more when the same amount of heat is applied. This uneven expansion is what causes the strip to bend. This concept is not just academic; everyday objects like bridges and railways employ expansion joints to accommodate thermal expansion and avoid structural damage.

• Thermal expansion is proportional to the original length and temperature change.
• Different materials have different coefficients of linear thermal expansion.
• Real-world applications include the engineering design of structures that experience temperature changes.

Physics Education

Constructive and engaging physics education is essential for developing a deep understanding of the natural world. It involves not just memorizing formulas and definitions, but also observing physical phenomena and conducting experiments. Experiences like watching a bimetallic strip react to heat bring physics theories to life and enhance the problem-solving skills of students.

Effective physics teaching often incorporates demonstrations that visualize abstract concepts like thermal expansion. This strategy helps students grasp more complex ideas later in their studies. Encouraging students to predict what will happen during such demonstrations, and then discussing the outcomes, fosters scientific inquiry and critical thinking.

• Interactive demonstrations such as bimetallic strip bending can significantly enhance the learning experience.
• Physics education underpins much of our modern technology and is essential for a scientifically literate society.
• Teachers aim to develop students' intuition for physical laws through observation and experimentation.