Heat & Temperature Questions & MCQ — Practice with Answers

Heat vs temperature

Heat and temperature are related but not the same thing. Heat is a form of energy — it can be transferred from one object to another. Temperature is a measurement of how hot or cold an object is (its degree of hotness). A large pot of warm water at 40 degrees Celsius contains more heat energy than a small cup of water at the same temperature, even though both have the same temperature. This is because the pot has a larger volume of water.

Heat flows from hotter to colder

Heat always flows from a hotter object or region to a colder one. This flow of heat continues until both objects reach the same temperature. For example, when you place a hot mug of tea on a table, the mug loses heat to the cooler surrounding air. The tea gradually cools down while the air around it warms up slightly, until they are at the same temperature. Heat never flows from a cold object to a hot object on its own.

Effects of heat gain and loss

When an object gains heat, two things can happen. First, it may expand — solids, liquids, and gases all increase in size when heated. This is why gaps are left between railway tracks, so the metal rails have room to expand on hot days without cracking. Second, it may change state — for example, ice (solid) melts into water (liquid) when it gains enough heat. When an object loses heat, the reverse happens: it contracts (decreases in size) and may change to a different state, such as water freezing into ice.

Good conductors of heat

Good conductors of heat are materials that allow heat to pass through them quickly and easily. Metals such as iron, copper, aluminium, and steel are good conductors of heat. This is why cooking pots and frying pans are made of metal — they conduct heat from the stove to the food efficiently. When you touch a metal railing on a hot day, it feels hot because it conducts heat from the Sun to your hand quickly.

Poor conductors of heat

Poor conductors of heat (sometimes called insulators) are materials that do not allow heat to pass through them easily. Examples include wood, plastics, air, and rubber. This is why the handles of cooking pots are often made of wood or plastic — they prevent heat from reaching your hand. A thermos flask uses trapped air (or a vacuum) to keep drinks hot or cold for longer, because air is a poor conductor of heat.

“Heat and temperature are the same thing.” Heat and temperature are different concepts. Heat is a form of energy that can be transferred between objects. Temperature is a measurement of the degree of hotness. Two objects can have the same temperature but contain different amounts of heat energy — for example, a bathtub of warm water contains much more heat energy than a cup of water at the same temperature, because it has a much larger volume.

“Metal objects are colder than wooden objects at room temperature.” At room temperature, a metal spoon and a wooden spoon are actually at the same temperature. The metal spoon only feels colder because metal is a good conductor of heat — it conducts heat away from your warm hand quickly. Wood is a poor conductor, so it does not draw heat from your hand as fast. The difference is in how quickly heat is transferred, not in the actual temperature of the objects.

“Cold flows into warm objects.” There is no such thing as “cold” flowing into an object. Only heat flows, and it always moves from a hotter object to a colder one. When you hold an ice cube, your hand feels cold because heat is flowing out of your warm hand into the colder ice. Your hand is losing heat — cold is not entering it.

“Bigger objects are always hotter.” The size of an object does not determine its temperature. A large block of ice is much bigger than a lit match, but the match has a much higher temperature. Size (volume) affects how much heat energy an object contains, but temperature measures the degree of hotness. A large object at a low temperature can contain more total heat energy than a small object at a high temperature, but the small object is still hotter.