Olympiad Science - Electricity and Circuits
Exam Duration: 45 Mins Total Questions : 30
If we touch a live wire carrying current, we get a shock. This is because our body is a/an
- (a)
conductor of electricity.
- (b)
insulator of electricity.
- (c)
source of electricity
- (d)
both (B) and (C).
Human body is a good conductor of electricity. So, the current passes through it and gets earthed, and gives us a shock in the process.
Electric heaters used for cooking have a filament or a heating coil placed on a plate made up of clay. Why is this so?
(i) It is a bad conductor of heat.
(ii) It is a bad conductor of electricity.
(iii) It is porous.
- (a)
Only (i) and (ii)
- (b)
Only (ii) and (iii)
- (c)
Only (i) and (iii)
- (d)
(i), (ii) and (iii)
Clay is a bad conductor of heat and electricity. In order to avoid shock due to the flow of current and also to avoid the instrument getting heated, a clay stand is used to place the coil or filament.
Why are the electric wires used in homes usually covered with materials like plastic or rubber?
- (a)
To prevent rusting
- (b)
To make handling easier
- (c)
To prevent shock and short circuits
- (d)
To make them look beautiful
Electric wires used in homes generally have a plastic or rubber covering so as to prevent shocks when we touch them. Insulation also prevents the two live wires coming in contact causing a short circuit.
Which of the following does NOT conduct electricity?
- (a)
Aluminium
- (b)
Salt solution
- (c)
Ceramic articles
- (d)
Silver
Ceramic articles do not conduct electricity.
Which of the following energy conversions take place in a torch?
- (a)
Electrical⟶chemical⟶light
- (b)
Chemical⟶electrical⟶light
- (c)
Electrical⟶light⟶chemical
- (d)
Light⟶chemical⟶electrical
A torchlight is powered by dry cells which convert chemical energy to electrical energy. This in turn, is converted into light energy by the torch light.
Why is tungsten used as a filament in electric bulbs?
- (a)
It is non-luminous.
- (b)
It is a soft metal
- (c)
It has a high melting point
- (d)
It has a low melting point.
Tungsten has a high melting point. Hence it is used as a filament in electric bulbs.
Identify the symbol of a fuse.
- (a)
- (b)
- (c)
- (d)
The symbol of a fuse is
Why is it unsafe to switch on a bulb with wet hands?
- (a)
It can give a shock.
- (b)
The bulb gets fused.
- (c)
The switch blows off.
- (d)
The wires are disconnected.
It is unsafe to switch on a bulb with wet hands because it can give a shock.
Which of the following statements is incorrect?
- (a)
A dry cell produces a small amount of electrical energy.
- (b)
A dry cell is used in TV remotes.
- (c)
All dry cells are rechargeable
- (d)
The symbol of a dry cell is
Only some dry cells are not rechargeable.
Which of the following cannot be used in electrical wires?
- (a)
Copper
- (b)
Silver
- (c)
Aluminium
- (d)
Iron
All the given metals are good conductors of electricity. But, iron cannot be used in electrical wires because it is brittle and corrodes when it comes in contact with the oxygen in the air.
Which components are required to make a simple electric circuit to light a bulb?
- (a)
Wires and a switch
- (b)
A cell and a switch
- (c)
A bulb and wires
- (d)
Wires, a cell, a bulb and a switch
A simple electric circuit consists of connecting wires, a cell, a bulb and a switch.
Which of the following is the symbol of an electric bulb?
- (a)
- (b)
- (c)
- (d)
The symbol of an electric bulb is shown below.
Why is copper NOT used as a filament?
- (a)
It produces white light
- (b)
It has a high melting point.
- (c)
It is a good conductor of current.
- (d)
It produces heat.
Copper cannot be used as a filament because it is a good conductor of current
Which one of the following is the correct grouping of different materials according to their electrical conductivity.
- (a)
Electrical Insulators Electrical Plastic, wood Mercury, tungsten - (b)
Electrical Insulators Electrical Conductors Carbon, steel Iron, paper - (c)
Electrical Insulators Electrical Conductors Copper, gold Nickel, clay - (d)
Electrical Insulators Electrical Conductors Iron, rubber Silver, plastic
Electrical insulators are plastic, wood, paper, clay, rubber, etc. Electrical conductors are metals like mercury, tungsten, steel, nickel, carbon, copper and gold.
Which of these are good electrical insulators?
- (a)
Graphite, wood, rubber
- (b)
Rubber, glass, wood
- (c)
Pure water, wood, silver
- (d)
Copper, iron, silver
Rubber, glass and wood are good electrical insulators.
Which of these will generate electric current when kept in sunlight but not in the dark?
- (a)
Dry cell
- (b)
Car battery
- (c)
Button cell
- (d)
Solar cell
A solar cell can generate electric current when kept in sunlight but not when kept in the dark.
Why doesn't a bulb glow even if the correct connections are made?
(i) Battery is dead.
(ii) Filament is broken.
(iii) Switch is closed
- (a)
Only (i)
- (b)
Only (ii)
- (c)
Only (iii)
- (d)
Only (i) and (ii)
If a battery is dead, the bulb does not get the supply of energy. So, the bulb does not glow. If the filament is broken in the bulb, it does not glow. But if a switch is closed, then the bulb glows as current flows through the circuit.
The bulb in a circuit glows when electric current.
- (a)
flows through its filament
- (b)
flows through the glass covering
- (c)
stops flowing to the bulb.
- (d)
flows into the air through the bulb.
The bulb in a circuit glows when electric current flows through the filament of the bulb.
What does a battery contain?
- (a)
A minimum of two terminals
- (b)
A minimum of three terminals
- (c)
A cell and a switch
- (d)
A bulb and a switch
A battery contains a minimum of two terminals
An electric cell
- (a)
converts electric energy into chemical energy.
- (b)
converts solar energy into chemical energy.
- (c)
converts chemical energy into electric energy.
- (d)
all of these.
An electric cell produces electricity from the chemicals stored inside it. It stops working when the stored 1 chemicals are used up due to irreversible change.
Electricity can be dangerous. A lot of caution should be exercised when handling electric objects. It is also very essential and must be conserved. Which one of these is not necessary?
- (a)
Never join the two terminals of the electric cell without connecting them with a switch and an electric device like a bulb.
- (b)
Never experiment with wires and sockets.
- (c)
Portable generators are dangerous too.
- (d)
none of these.
The two terminals of the electric cell should never be joined without connecting them with a switch and 1 an electric device like a bulb as this leads to wastage of stored chemical energy. Wires and sockets may be carrying a lot of electric current. Carelessness in handling electricity can even cause death. 1 Portable generators also have a lot of current which can give an electric shock. All the statements are correct and essential.
Electric cells can be used in
- (a)
alarm clocks and wrist
- (b)
radios and transistors. watches.
- (c)
cameras.
- (d)
all of these.
An electric cell provides electric energy to these devices to do their work.
An electric bulb contains
- (a)
a filament.
- (b)
a positive terminal.
- (c)
a negative terminal.
- (d)
all of these.
The filament is fixed to two wires which form two terminals. One of the wires is connected to the metal case at the base of the bulb. The other wire is connected to the metal tip at the centre of the base. These two terminals do not touch each other the filament is fixed to two wires which form two terminals. One of the wires is connected to the metal case at the base of the bulb. The other wire is connected to the metal tip at the centre of the base. These two terminals do not touch each other.
The direction of current in an electric circuit is from
- (a)
the positive to the negative terminal of the electric cell.
- (b)
the negative to the positive terminal of the electric cell.
- (c)
both 'a' and 'b'.
- (d)
none of these
In an electric circuit the direction of the flow of current is taken from the positive to the negative terminal of the electric cell.
An electric bulb may not glow if
- (a)
the bulb is fused.
- (b)
the filament is broken.
- (c)
the crcuit is broken.
- (d)
all of these.
The circuit may be broken if the wires are not connected properly.
When a bulb glows
- (a)
light is produced.
- (b)
Heat produced
- (c)
electric energy is converted into light and heat energy.
- (d)
all of these.
There is a transformation of energy when a bulb glows.
Which one of the following is a good conductor of electricity?
- (a)
salt solution
- (b)
mercury
- (c)
graphite
- (d)
all of these
Conductors are materials which allow electric current to pass through them easily. All metals are good conductors of electricity. Mercury is a liquid metal at room temperature. Graphite is widely used in making pencils as it leaves a mark on paper. So you can sharpen your pencil on both sides and use it as a conductor of electricity. Pure water is a non-conductor of electricity. Normally the water we get has some salt dissolved in it which makes it a conductor of electricity. A salt solution is a good conductor of electricity.
Which one of the following is an insulator?
- (a)
dental floss wire
- (b)
wood
- (c)
mica
- (d)
all of these
Plastic, rubber, mica, Bakelite, ebonite, air, pure distilled water, etc. do not allow electricity to pass through them. Therefore, insulating materials are made using these substances. Insulators act as safety devices as they prevent electric fires and electric shocks.
A screw driver used by an electrician has a
- (a)
a plastic handle.
- (b)
a metallic working part.
- (c)
insulator.
- (d)
all of these.
The plastic handle acts as an insulator and prevents electric shock while working. A screw driver is an essential tool of an electrician.
Select the right match
Column I | Column II |
i) First electric cell | A) moist paste of dry cell |
ii) Ammonium chloride | B) mercury |
iii) Liquid metal | C) Volta |
- (a)
i-C; ii-A; iii-B
- (b)
i-B; ii-A; iii-C
- (c)
i-A; ii-B; iii-C
- (d)
i-B; ii-C; iii-A
Volta invented the first electric cell around 1800 A.D. Mercury is a liquid metal and is a good conductor of electricity. A dry or Leclanche cell is a zinc container which contains a moist paste of ammonium chloride. It also has in its centre a carbon rod fitted with a metal cap and wrapped in a muslin cloth bag. The muslin cloth bag contains a mixture of powdered coke, graphite, zinc chloride and manganese dioxide.