Free Electric Current and Its Effects 01 Practice Test - 7th grade
Question 1
The amount of heat produced in a conductor does not depend on __________.
length
material
force
thickness
SOLUTION
Solution : C
The amount of heat produced in a conductor depends on the following parameters:
1. Material (resistance offered by the material) – good conductors produce less heat; e.g., elements of electric appliances are made of nichrome whereas connecting wires are made up of copper which is a better conductor so they do not get heated up easily.
2. Length – as length increases the heat produced also increases; e.g., heating elements are coiled in heaters to increase their length.
3. Thickness – as thickness increases the heat produced decreases; e.g., wires of iron are thicker than normal connecting wire so they don’t get heated up easily.
Force is not a parameter to be considered in this case.
Question 2
Metals good conductors of electricity because they possess:
No electrons
Free electrons
Free protons
Free neutrons
SOLUTION
Solution : B
Metals are good conductors of electricity because they possess free electrons. These free electrons help in the flow of current through the conductor.
Question 3
Which of the following devices use electromagnet?
SOLUTION
Solution : C
When electric current is passed through a coiled conductor, it behaves like a magnet. It is called an electromagnet. An electric bell uses an electromagnet which is responsible for attracting the striker in the bell.
Question 4
Which of the following can conduct electricity?
Wood
Plastic
Human body
SOLUTION
Solution : D
Human body can conduct electricity due to presence of blood which is a medium of high ion content. Due to the presence of minerals and ions, blood proves to be a very good conductor of electricity. Wood, plastic and rubber are poor conductors of electricity.
Question 5
How many cells of 1.5 V will be needed to make a 9 V battery?
2
4
6
8
SOLUTION
Solution : C
Let the number of required cells be N. The total voltage is equal to 9 volt.
Therefore, 1.5×N=9
N=91.5=6
Hence 6 cells will be required.
Question 6
Which of the following particle is responsible for the electric current in a wire?
Neutron
Positron
Proton
Electron
SOLUTION
Solution : D
An electric current is the rate of flow of charge per unit time. The movement of electrons in a wire constitutes the electric current. Protons and neutrons are situated inside the nucleus of an atom. The moving charged particles in electric current are called charge carriers.
Question 7
What does the above symbol represent?
SOLUTION
Solution : C
The above symbol is used to represent a bulb in an electric circuit.
An electric bulb consists of a transparent glass casing containing a wire filament (usually tungsten) that emits light due to the heating effect of electricity.
Question 8
Which of the following is the symbol of an electric battery?
SOLUTION
Solution : B
Battery is a device with two or more electric cells connected in series.
Question 9
Electromagnets are permanent magnets.
SOLUTION
Solution : B
Electromagnets behave as magnets only when an electric current is passed through them. As soon as the current supply is switched off, it loses its magnetic properties. Magnetic materials like iron and steel are used to make electromagnets.
Question 10
Which of the following devices consumes least electrical energy for the same light intensity?
SOLUTION
Solution : D
Incandescent electric bulbs are often used as lighting sources but they also give away more heat. This is not desirable as it results in the wastage of electricity. The fluorescent tube-lights and compact fluorescent lamps (CFLs) are efficient lighting sources than incandescent bulbs. Nowadays, the use of light emitting diode (LED) bulbs is increasing. For producing a given intensity of light, LED bulbs consume less energy as compared to other types of bulbs.