Unit 13
Electric
Current and Circuits
Short Questions:
Q1. What is an electric
current?
An electric current is
a flow of electrons through a conductor
such as metal.
Q2. What are semi-
conductors?
Semi-conductors are in
between materials. They are insulators when warm. They are used in microchips
in computers and other electronics equipment.
e.g., calculators and
watches.
Q3. What is circuit?
The conducting path
through the bulb, wires and cell is called a circuit.
Q4. What job does a
cell or battery do in a circuit?
A cell or battery can
make electrons to move.
Q5. What is difference
between voltmeter and ammeter?
Ammeter:
It is an instrument
which gives an accurate measurement of the electric current flowing in a
circuit.
Voltmeter:
It is an instrument
which gives an accurate measurement of the volts.
Q6. What is resistance?
Why do we use resistors?
The property of
substance which offer opposition to the flow of current through it is called
its resistance.
Q7. What is
electrolysis?
Electricity can be used
to decompose(split) certain compounds. This process is called electrolysis.
Q8. What effect does
electric current have on chemicals?
It ionizes the chemical
when it pass through the chemicals.
Q9. Write the three
safety rules while using the electricity?
i.
Never use an
electrical appliance while standing in water or when your hands are wet.
ii.
Never run a wire
under a carpet.
iii.
Do not overload
power sockets.
Q10. What is fuse? What
is its purpose?
It is simply an
enclosed length of wire that has a low melting point. It forms the weakest link
in a circuit. When a current that is too large passes through the fuse, it
heats up and melts, causing a break in the circuit before a fire can develop.
Q11. How miniature
circuit breakers work?
It is small
electromagnetic switch. When the electric current is at a safe level, it can
flow safely through the circuit breaker. If the current reaches unsafe level, the
electromagnet is then powerful enough to pull the halves of the switch apart.
The circuit is broken and electricity shuts off.
Long Questions:
Define resistor?
Explain its types?
Resistors:
A resistor is a part of
an electrical circuit that is put there to limit the amount of electric current
that flows through the circuit.
Types of resistors:
There are two types of
resistors.
Fixed resistors:
Fixed resistors have a
set resistance. They are mainly used to reduce that flow of electricity through
a circuit and reduce the dangers caused by overheating.
Variable resistors:
A variable resistor
contains a long coil of nichrome wire. A variable resistor is being used to
control the brightness of a bulb. A variable resistor can be used to dim the
lights in a room. The volume control on a typical radio is also a variable
resistor, while some model electric car and train sets also use a variable
resistor to control the speed of the car or train.
Q2. What are parallel
and series circuit? Also write their advantages and disadvantages?
Series circuit:
When the bulbs are
arranged in series(in line). The circuit is called series circuit. Advantages:
i.
The circuit from
the cell passes through each bulb in turn.
ii.
The current is
the same at all points in the circuit.
Disadvantages:
i.
The bulb glow
dimly.
ii.
It is more
difficult for the electrons to pass through two bulbs than one.
Parallel circuit:
They are arranged on
many paths electricity can travel from one end of the cell through many
branches to the other end of the cell.
Advantages:
i.
If one bulb is
removed other will keep glowing brightly.
ii.
We can use
separate switch for each bulb.
Disadvantages:
i.
As each bulb is
getting the full voltage from the cell, so it takes more voltage. So cell or
battery will not last long.
ii.
The current is
not the same in all parts of the circuit.
