Physics

Heat natural travels

• from cold to hot objects

• from hot to cold objects

• from/to objects of the same tempretature

• cannot be predicted

Answer explanation

The atoms in the hot bodies have higher kinetic energy than those of the cold bodies. Thus to maintain thermal equilibrium, the atoms of higher kinetic energy tries to move and collide with the atoms of low kinetic energy. Thus heat transfers from a hot body to a cold body. (Second Law of Thermodynamics)

Heat is:

• a temperature difference

• energy content of an object

• a property objects have by virtue of their temperatures

• energy transferred by virtue of a temperature difference

Answer explanation

Heat is the form of energy that is transferred between two substances at different temperatures. The direction of energy flow is from the substance of higher temperature to the substance of lower temperature. Heat is measured in units of energy, usually calories or joules.

Running a refrigerator with its door open in a hot room makes the room

• cooler

• warmer

• either A or B

• neither A or B

Answer explanation

A refrigerator is a heat engine it extracts heat from low temperature reservoir and transfer it to high temperature. If a refrigerator’s door is kept open, then room will become hot, because then refrigerator exhaust more heat into the room than earlier. In this way, temperature of the room increases and room becomes hot. No refrigerator is efficient. Thus it exhaust more heat into the room than it extract from it. Thus, a room cannot be cooled by keeping the door of a refrigerator open. (CONVECTION)

Your grandmother places a pitcher of iced tea next to a plate of warm, freshly baked cookies so that the pitcher and the plate are touching. You tell your grandmother that the plates are in thermal contact, which means that

• heat flows from the cold pitcher to the warm plate

• heat flows from the warm plate to the cold pitcher

• heat flows within the warm plate but not within the cold pitcher

• heat flow from the warm plate to the cold pitcher and from the cold pitcher to the warm plate

Answer explanation

Both the plate and the pitcher together is a system where heat transfer is able between both objects. In this case the plate is able to transfer its thermal energy or heat to the pitcher of ice.

Energy transfer by convection is primarily restricted to one of these

• fluids

• gases

• liquids

• solids

Answer explanation

Energy transfer by convection is primarily restricted to fluids. Fluids can be both liquids and gases.

The higher the temperature of an object, the

• lesser the wavelengths it radiates

• longer the wavelengths it radiates

• more wavelength is radiates

• shorter the wavelenghts it radiates

Answer explanation

While all objects emit radiation at all wavelengths, the amount of radiation emitted usually peaks at a certain wavelength. The wavelength of peak emission depends on the temperature of the object emitting radiation. A higher temperature will cause the wavelength of peak emission to be at a shorter wavelength. Wavelength is inversely proportional to temperature. Because temperature is related to energy. As wavelength increases, temperature decreases.

What kind of waves causes the particles over which they pass to vibrate at right angles(perpendicular) to the direction of wave motion?

• diffracted waves

• longitudinal waves

• polarized waves

• transverse waves

Answer explanation

Transverse wave is one classification of mechanical waves that need a medium/material to propagate (move)

Which of the following colors ofl ight has the shortest wavelength?

• blue

• green

• white

• yellow

Answer explanation

Visible lights is the main reason why we see different colors (ROYGBIV). Always remember that frequency/energy is inversely proportional to wavelength. For example, if you see a rainbow after a rain the most visible color is red and violet is hard to be seen. The more visible the color, the longer the wavelength. The less visible color, the shorter the wavelength. Hence, the shorter the wavelength the higher the frequency/energy.

What is transferred by a wave from one point to another?

• energy

• mass of the medium

• particles of the medium

• volume of the medium

What happens to the frequency of a train'swhistle as it gets closer to the observer?

• decreases

• increases

• reamins the same

• resonates

Answer explanation

Frequency-pitch

The shorter the wavelength, the higher the frequency, and the higher the pitch, of the sound. In other words, short waves sound high; long waves sound low.