Which one of the following elements is used in solar cells?
Correct Answer:
(A)
Silicon
Solar cells are the components of solar arrays that convert radiant light from the sun into electricity that is then used to power electrical devices. Solar cells contain materials with semiconducting properties in which their electrons become excited and turned into an electrical current when struck by sunlight. While there is a dozen of variation of solar cells, the two most common types are those made of crystalline silicon (both monocrystalline and polycrystalline) and those made with what is called thin film technology. The majority (90 %) of the solar cells on the market today are made of silicon.
Ques:
2
Photovoltaic cells are:
Correct Answer:
(A)
Solar cells
The conversion of light energy into electrical energy is based on the phenomenon called photovoltaic effect. A photovoltaic cell is the basic unit of the system where the photovoltaic effect is utilized to produce electricity from light energy. Silicon is most widely used semiconductor material for constructing photovoltaic cell.
Ques:
3
Consider the following statements:
Assertion (A): Copper rods are generally preferred to iron rods for making lightning conductors.
Reason (R): Copper is better conductor of electricity than iron and is not easily oxidized under atmospheric conditions.
Code:
(A) and (R) are true and (R) is the correct explanation of
(A).
Correct Answer:
(A)
and (R) are true, but (R) is not the correct explanation of
Copper rods are preferred for making lightning conductor because:
Copper is a better conductor than iron.
Copper is not easily oxidized in the presence of oxygen and water molecules while iron gets rusted.
Loss of energy is much less with a copper rod than with iron rod, as copper is a bad conductor of heat than iron.
Ques:
4
The characteristic of superconductor is –
Correct Answer:
(C)
Zero permeability
In electromagnetism, permeability is a property of a material that describes the ability of a material to support the formation of a magnetic field within itself or we can say that it is the degree of magnetization that a material obtains in response to an applied magnetics field. It is represented by Greek letter m (Mu). The permeability and electrical resistance of the superconductor is zero.
Ques:
5
At which temperature superconductivity can be of tremendous economic interest saving billions of rupees?
Correct Answer:
(C)
at room temperature
If we could achieve superconductivity at room temperature then we can save billions of rupees through electric transmission without any power loss.
Ques:
6
Electric conduction in a semiconductor takes place due to-
Correct Answer:
(C)
Both electrons and holes
When electric field is applied across a semiconductor, the current conduction takes place by free electrons and holes. The free electrons are produced due to the breaking up of some covalent bonds by thermal energy. At the same times holes are created in the covalent bonds. Under the influence of electric field, conduction takes place by these free electrons and holes. The conducting properties of a semiconductor can be increased by adding small amount of suitable impurities to it.
Ques:
7
A 100-watt electric bulb is used for 10 hours. What will be the cost of electricity consumed, if the consumption cost is Rs. 5 per unit?
Correct Answer:
(A)
Rs. 5
Energy Consumption of 100-watt electric bulb which is used for 10 hours = 100 ×10
= 1000-watt hour
= 1 kilowatt hour
= 1 unit.
According to question the cost of 1 unit of electricity = Rs 5.
Correct Answer:
(A)
There is no heat loss
When electrical energy is converted into motion, there is no heat loss.
Ques:
10
Electric motors operating at low voltages tend to burn out because –
Correct Answer:
(A)
They draw more current which is inversely proportional to the voltage.
Electric motors operating at low voltages tend to burn out because they draw more current which is inversely proportional to the voltage.