English Medium Class 10 - CBSE Important Questions for Science

Answer the following question.
Write the mathematical expression for Joule's law of heating.

Solve the following question.
Compute the heat generated while transferring 96000 coulombs of charge in two hours through a potential difference of 40 V.

The resistance of a wire of 0.01 cm radius is 10 Ω. If the resistivity of the wire is 50 × 10^-8 Ω, find the length of this wire.

What is the meaning of electric power of an electrical device? Write its SI unit.

An electric kettle of 2 kW is used for 2h. Calculate the energy consumed in 

1. kilowatt hour and
2. joules.

A student wants to use an electric heater, an electric bulb and an electric fan simultaneously.

How should these gadgets be connected with the mains? Justify your answer giving three reasons.

What is meant by resistance of a conductor ? Define its SI unit.

How will the resistance of a wire be affected if its

1. length is doubled, and
2. radius is also doubled ?

Give justification for your answer.

The resistance of a resistor is reduced to half of its initial value. If other parameters of the electrical circuit remain unaltered, the amount of heat produced in the resistor will become ______.

As shown in the diagram an aluminium rod 'AB' is suspended horizontally between the two poles of a strong horse shoe magnet in such a way that the axis of rod is horizontal and the direction of the magnetic field is vertically upward. The rod is connected in series with a battery and a key.

State giving reason:

1. What is observed when a current is passed through the aluminium rod from end B to end A?
2. What change is observed in a situation in which the axis of the rod 'AB' is moved and aligned parallel to the magnetic field and current is passed in the rod in the same direction?

When does a solenoid behave as a magnet? Draw the pattern of the magnetic field produced inside it showing the directions of the magnetic field lines.

Two LED bulbs of 12W and 6W are connected in series. If the current through 12W bulb is 0.06A the current through 6W bulb will be ______.

The correct pattern of magnetic field lines of the field produced by a current carrying circular loop is:

Assertion (A): A current carrying straight conductor experiences a force when placed perpendicular to the direction of magnetic field.

Reason (R): The net charge on a current carrying conductor is always zero.

Give reason to justify the following: Flow of energy in a food chain is unidirectional.

"Our food grains such as wheat and rice, the vegetables and fruits and even meat are found to contain varying amounts of pesticide residues." State the reason to explain how and why it happens?

Explain how the pesticides enter a food chain and subsequently get into our body.

Human body is made up of five important components, of which water is the main component. Food, as well as potable water, are essential for every human being. The food is obtained from plants through agriculture. Pesticides are being used extensively for a high yield in the fields. These pesticides are absorbed by the plants from the soil along with water and minerals and from the water bodies these pesticides are taken up by the aquatic animals and plants. As these chemicals are not biodegradables, they get accumulated progressively at each trophic level. The maximum concentration of these chemicals gets accumulated in our bodies and greatly affects the health of our mind and body.

1. Why is the maximum concentration of pesticides found in human beings?  (1)
2. Give one method which could be applied to reduce our intake of pesticides through food to some extent.  (1)
3. Various steps in a food chain represent: 
   1. Food web
   2. Trophic level
   3. Ecosystem
   4. Biomagnification  (1)
4. With regard to various food chains operating in an ecosystem, man is a:
   1. Consumer
   2. Producer
   3. Producer and consumer
   4. Producer and decomposer  (1)

Assertion (A): The energy which passes to the herbivores does not come back to autotrophs.

Reason (R): The flow of energy in a food chain is unidirectional.

Use of several pesticides which results in excessive accumulation of pesticides in rivers of ponds, is a matter of deep concern. Justify this statement.