Olympiad Test: Work, Force And Energy -2 - Class 4 MCQ

- The correct gadget for measuring temperature is the thermometer.
- A thermometer works by using materials that change in response to temperature changes, such as mercury or alcohol in glass thermometers, which expand or contract.
- Digital thermometers use electronic sensors to provide precise temperature readings.
- Other options like a stopwatch, scale, and measuring jar are used for time, weight, and volume measurements, respectively, not temperature.

A calorimeter is a scientific instrument used to measure the heat released or absorbed during a chemical or physical process. It helps in determining the energy content of a substance by measuring the temperature change that occurs when the substance undergoes a chemical reaction or experiences a physical change.

All the options provided are indeed SI units of measure. Here's an explanation for each:

1. Watt (W): The SI unit of power, representing the rate of energy transfer. It is defined as one joule per second (1 W = 1 J/s).

2. Newton (N): The SI unit of force. It is defined as the force required to accelerate a one-kilogram mass by one meter per second squared (1 N = 1 kg·m/s²).

3. Joule (J): The SI unit of energy. It is defined as the amount of energy transferred when a force of one newton is applied over a distance of one meter (1 J = 1 N·m).

Since all of these units are part of the International System of Units (SI), the correct answer to the question of which is NOT an SI unit of measure is:

4. None

4. Headphones

Headphones use electromagnets to convert electrical signals into sound. When an electric current passes through the coils of wire in the headphones, it creates a magnetic field that moves the diaphragm to produce sound.

• Lamp: Typically uses an incandescent bulb or LED, not an electromagnet.
• Electric stove: Uses heating elements rather than electromagnets.
• Compass: Uses a permanent magnet, not an electromagnet.

So, the correct answer is:

4. Headphones

For a freely falling object, the mechanical energy is the sum of its potential and kinetic energy. As the object falls, its potential energy decreases while its kinetic energy increases. The total mechanical energy of the object (assuming no air resistance) remains constant and is equal to the sum of its potential and kinetic energy at any point during the fall.

The correct description is that the mechanical energy of the object is actually constant and is not the difference between potential and kinetic energy. Therefore, none of the options provided accurately describe the mechanical energy in the context of this problem.