Science 3 Marks Question

Since, it is a fact that the water present in the ocean (near the equator) is heated by the sun to a very higher temperature than the water near the poles of the earth. It is due to the falling of the sun rays perpendicularly in the equatorial region. So, in the equatorial region, the ocean water expands and becomes lighter. While on the other side, the water in the polar region remains cold and heavy. It leads to the flow of convection currents of heat of warm water from the equator towards the poles. Heat of the cold water flow from the poles towards the equator just below the surface of ocean. So, these types of currents are known as oceanic currents.

We wear dark coloured clothes in winter to keep us warm as they absorb all the heat radiation coming from the sun whereas light coloured clothes reflect most of the heat radiation coming from the sun that falls on them and therefore we feel more comfortable wearing them in the summer.

1. Mercury expands evenly as the temperature rises.
2. It is a good conductor of heat.
3. It is silvery white and can be seen from outside the glass.
4. It does not stick to glass.

For the setting of curd at places where temperature is below room temperature, the container in which curd is to be made, must be kept in a thermally insulated cover or it can be wrapped either by a woollen material or a jute sack so that temperature is maintained for the setting of curd. The container can also be kept in the sun or near the gas stove while cooking food for the setting of curd.

The effects of heat are:

1. When an object is heated, then it becomes hotter and may get expand. So, in this heat may change the state of the body like ice can also get change into the water.
2. Heat sometimes acts as a catalyst to speed up the chemical reaction.
3. Heat can even kill the bacteria as well.

During winters, we prefer wearing more layers of clothing than just one thick piece of clothing because air gets trapped in between the various clothing layers. Being a poor conductor of heat, air prevents heat loss from our body. Hence, layers of clothing keep us warmer than a single layer.

Due to following reasons, mercury is used in the thermometers instead of water:

1. When the thermometer breaks, the mercury can be easily collected.
2. Mercury can has more expansion than the water.
3. Also, mercury do not stick on the walls of thermometer like water.

During the day, the land gets heated faster than the water. The air over theland becomes hotter and rises up. The cooler air from the sea rushes in towards the land to take its place. The warm air from the land moves towards the sea to complete the cycle. The air from the sea is called the sea breeze.

• Laboratory thermometer and the clinical thermometer consist of a long, narrow, uniform glass tube.
• Laboratory thermometer and the clinical thermometer have a bulb containing mercury at the end of the tube.
• Laboratory thermometer and the clinical thermometer are marked with Celsius scale on the glass tube.

The particles of water become more lighter and rise up in the middle. Due to this, the cold particles of water which are heavier come down along the sides of the vessel. So, the convection currents of heat are setup and water becomes hot. The moment, when the heat is applied at the top, then the water present in the upper portion becomes hot and these hot water molecules get fixed over the surface. Since, water is a bad conductor of heat, due to which water present at the lower end (or bottom) of the vessel remains.

In places of hot climate, it is advised to paint the outer walls of houses as white because a light colour such as white reflects back most of the heat that falls on it. Hence, a light colour tends to keep the house cool.

The water is poor conductor of heat so do not heated by conduction. When water is heated, the water became lighter. Hot water rises up. The cold water from the sides moves down towards the source of heat. This water also gets hot and rises upward and water from the sides moves down. This process continues till the whole water gets heated. This mode of heat transfer is known as convection.

1. Transfer of heat from burner to pan is by radiation.
2. Transfer of heat from pan to water is by conduction.
3. Transfer of heat within water is by convection.