CBSE Class 10th...

Find the focal length of a convex mirror whose radius of curvature is 32 cm ?

A concave mirror produces three times magnified real image of an object placed at 10 cm in front of it. The position of image is :

Assertion (A): The process of copying the DNA will have some variations each time.

Reasons (R): No bio- chemical reaction is absolutely reliable.

Assertion (A): The micro- organisms, comprising bacteria and fungi, breakdown the dead remains and waste products of organisms.

Reasons (R): Decomposers break-down the complex organic substances into simple inorganic substances that go into the soil and are used up once more by the plants.

Assertion (A): In Newlands’s octaves, the properties of lithium and sodium were found to be same.

Reasons (R): Sodium is the eighth element after lithium. 

Light enters from air to glass having refractive index 1.5.Then, the speed of light in the glass is :

A concave lens has a focal length of 15 cm. At what distance should the object from the lens be placed so that it forms an image at 10 cm from the lens ?

The length and complexity of food chains vary greatly. Each organism is generally eaten by two or more other kinds of organisms which in turn are eaten by several other organisms. So, instead of a straight-line food chain, the relationship can be shown as a series of branching lines called a food web.

The greatest number in trophic levels of food chain is of:

The length and complexity of food chains vary greatly. Each organism is generally eaten by two or more other kinds of organisms which in turn are eaten by several other organisms. So, instead of a straight-line food chain, the relationship can be shown as a series of branching lines called a food web.

Green plants in a terrestrial ecosystem capture ___________of the energy of sunlight that falls on their leaves and convert it into food energy.

The length and complexity of food chains vary greatly. Each organism is generally eaten by two or more other kinds of organisms which in turn are eaten by several other organisms. So, instead of a straight-line food chain, the relationship can be shown as a series of branching lines called a food web.

Biological magnification is greatest in:

The length and complexity of food chains vary greatly. Each organism is generally eaten by two or more other kinds of organisms which in turn are eaten by several other organisms. So, instead of a straight-line food chain, the relationship can be shown as a series of branching lines called a food web.

Decomposers comprises of:

The length and complexity of food chains vary greatly. Each organism is generally eaten by two or more other kinds of organisms which in turn are eaten by several other organisms. So, instead of a straight-line food chain, the relationship can be shown as a series of branching lines called a food web.

Flow of energy in food web is unidirectional. This implies:

The acid produced during ant sting is :

Vanilla is an olfactory indicator. The smell of vanilla vanishes with :

In paramecium, which is also a unicellular organism, the cell has a definite shape and food is taken in at a specific spot. Food is moved to this spot by the movement of cilia, which cover the entire surface of the cell.

Depending on their environmental conditions, a paramecia can reproduce:

In paramecium, which is also a unicellular organism, the cell has a definite shape and food is taken in at a specific spot. Food is moved to this spot by the movement of cilia, which cover the entire surface of the cell.

The significant advantages of conjugation for paramecium is:

In paramecium, which is also a unicellular organism, the cell has a definite shape and food is taken in at a specific spot. Food is moved to this spot by the movement of cilia, which cover the entire surface of the cell.

The mutualistic relationship between paramecium and algae is called:

In paramecium, which is also a unicellular organism, the cell has a definite shape and food is taken in at a specific spot. Food is moved to this spot by the movement of cilia, which cover the entire surface of the cell.

Paramecium cell moves and collects food using:

In paramecium, which is also a unicellular organism, the cell has a definite shape and food is taken in at a specific spot. Food is moved to this spot by the movement of cilia, which cover the entire surface of the cell.

The “Specific spot” to take in food, is:

In teeth, the bacteria, acid, food debris, and saliva combine to form :

The oxides of metals that are low in the activity series can be reduced to metals by :

Alloying is a very good method of improving the properties of a metal. We can get the desired properties by this method. For example, iron is the most widely used metal. But it is never used in its pure state. This is because pure iron is very soft and stretches easily when hot. But, if it is mixed with a small amount of carbon (about 0.05%), it becomes hard and strong.

When iron is mixed with nickel and chromium, we get:

Alloying is a very good method of improving the properties of a metal. We can get the desired properties by this method. For example, iron is the most widely used metal. But it is never used in its pure state. This is because pure iron is very soft and stretches easily when hot. But, if it is mixed with a small amount of carbon (about 0.05%), it becomes hard and strong.

Alloying is done:

Alloying is a very good method of improving the properties of a metal. We can get the desired properties by this method. For example, iron is the most widely used metal. But it is never used in its pure state. This is because pure iron is very soft and stretches easily when hot. But, if it is mixed with a small amount of carbon (about 0.05%), it becomes hard and strong.

We know alloying is done to make the metal rust free. When iron is coated with zinc, process is called:

Alloying is a very good method of improving the properties of a metal. We can get the desired properties by this method. For example, iron is the most widely used metal. But it is never used in its pure state. This is because pure iron is very soft and stretches easily when hot. But, if it is mixed with a small amount of carbon (about 0.05%), it becomes hard and strong.

The galvanised article is protected against rusting even if the zinc coating is broken. This is because:

Alloying is a very good method of improving the properties of a metal. We can get the desired properties by this method. For example, iron is the most widely used metal. But it is never used in its pure state. This is because pure iron is very soft and stretches easily when hot. But, if it is mixed with a small amount of carbon (about 0.05%), it becomes hard and strong.

We don’t want gold to be of 24 carats, as it is very soft. To make it suitable for jewellery, we alloy gold with:

A non-metal which is lustrous is :

When zinc is added to solution of Iron (II) sulphate, the colour of iron sulphate changes from green to :

Electromagnets are made out of a coil of wire (wire curled in series). This is more effective in producing a magnetic field than just a wire running straight. The magnetic field disappears when the current is turned off. MRI scan uses electromagnets.

Magnetic strength of an electromagnet can be easily altered by:

Electromagnets are made out of a coil of wire (wire curled in series). This is more effective in producing a magnetic field than just a wire running straight. The magnetic field disappears when the current is turned off. MRI scan uses electromagnets.

Advantage of electromagnet over bar magnet is:

Electromagnets are made out of a coil of wire (wire curled in series). This is more effective in producing a magnetic field than just a wire running straight. The magnetic field disappears when the current is turned off. MRI scan uses electromagnets.

One disadvantage of electromagnet over bar magnet is:

Electromagnets are made out of a coil of wire (wire curled in series). This is more effective in producing a magnetic field than just a wire running straight. The magnetic field disappears when the current is turned off. MRI scan uses electromagnets.

Mobiles and telephones uses:

Electromagnets are made out of a coil of wire (wire curled in series). This is more effective in producing a magnetic field than just a wire running straight. The magnetic field disappears when the current is turned off. MRI scan uses electromagnets.

Full form of MRI is:

Which metals do not corrode easily ?

Aqua regia is a mixture of concentrated hydrochloric acid and nitric acid in the ratio :