Extra 30 short-answer questions for the chapter:11 "Electricity" in Class 10 CBSE Science:
Define electric current. Write its SI unit.
Answer:
Electric current is the
flow of electric charge
in a conductor per unit time.
Formula:
I=
QtI
= \frac{Q}{
t}I
=
tQ
(where III is current, QQQ is charge,
ttt
is time).
SI Unit:
Ampere (A).
Define electric potential and potential difference. What is its SI unit?
Answer:
Electric potential
at a point is the work done in bringing a unit positive charge from infinity to that point.
Potential difference
is the work done to move a unit charge between two points in a circuit.
Formula:
V=WQV = \frac{W}{
Q}V
=QW
SI Unit:
Volt (V).
What is Ohm’s Law? Write its mathematical expression.
Answer:
Ohm’s law states that
the current flowing through a conductor is directly proportional to the voltage across it, provided the temperature remains constant
.
Formula:
V=IRV = IRV=IR
What is the SI unit of resistance? Define it.
Answer:
SI unit of resistance
is
Ohm (Ω)
.
Definition:
A conductor has
1 Ohm resistance
if a
1V potential difference
across it produces
1A current
.
List three factors affecting the resistance of a conductor.
Answer:
Length (L):
Resistance increases with length.
Cross-sectional area (A):
Resistance decreases with an increase in area.
Material of the conductor:
Different materials have different resistivities.
Define resistivity and give its SI unit.
Answer:
Resistivity (ρ\
rhoρ
)
is the resistance of a material per unit length and unit cross-sectional area.
Formula:
R=
ρLAR
= \rho \frac{L}{
A}R
=
ρAL
SI unit:
Ohm-meter (
Ωm
).
Why are copper and
aluminium
used for making electrical wires?
Answer:
Copper and
aluminium
have
low resistivity
, which allows
better conductivity
.
They are
ductile
and can be easily drawn into wires.
Why is tungsten used in filament bulbs?
Answer:
Tungsten has a
high melting point (≈ 3380°C)
and
high resistivity
, which allows it to glow without melting.
Why are electrical appliances connected in parallel?
Answer:
In a parallel circuit:
Voltage remains constant
across all devices.
If one appliance stops working, others
continue functioning
.
It
reduces the effective resistance
, allowing higher current flow.
What happens to resistance if the length of a wire is doubled?
Answer:
Resistance is directly proportional to length
(R
∝
LR \
propto
LR
∝
L).
If the length is doubled, resistance
also doubles
.
Derive the formula for the total resistance of resistors in series.
Answer:
In series, current remains
same
, but voltage divides:
V=V1+V2+V3V = V_1 + V_2 + V_3V=V1+V2+V3
IR=IR1+IR2+IR3IR = IR_1 + IR_2 + IR_3IR=IR1+IR2+IR3
Rtotal
=R1+R2+R3R_{\text{total}} = R_1 + R_2 + R_3Rtotal=R1+R2+R3.
How does resistance change in a parallel combination?
Answer:
In a parallel circuit, voltage remains the
same
, but current divides.
Formula:
1Rtotal=1R1+1R2+1R3\frac{
1}{
R_{\text{total}}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}
Rtotal
1=R11+R21+R31
Compare series and parallel circuits.
Answer:
Series Circuit:
Current remains
same
.
Total resistance
increases
.
If one component fails, the circuit is
broken
.
Parallel Circuit:
Voltage remains
same
.
Total resistance
decreases
.
If one component fails, others
continue working
.
Define electric power and its SI unit.
Answer:
Electric power (P)
is the rate at which electrical energy is consumed.
Formula:
P=VIP = VIP=VI or P=I2RP = I^2RP=I2R or P=V2/RP = V^2/RP=V2/R.
SI unit:
Watt (W).
What is the commercial unit of electrical energy?
Answer:
Commercial unit:
Kilowatt-hour (kWh).
1 kWh = 1000W × 3600s = 3.6×1063.6 \times 10^63.6×106 J
.
Why is electrical power transmitted at high voltage?
Answer:
To
reduce power loss
due to heat.
Power loss = I2RI^2RI2R
, so reducing current minimizes energy loss.
Why is nichrome used in heating elements?
Answer:
Nichrome has
high resistivity
and
high melting point
, making it suitable for heaters.
What is a fuse? Why is it used in an electric circuit?
Answer:
A
fuse
is a safety device that
breaks the circuit
if the current exceeds a safe limit.
Made of
low melting point
materials (like tin-lead alloy).
State Joule’s law of heating.
Answer:
Heat produced (H) = I2RtI^2 R tI2Rt
.
More current, resistance, or time increases heating.
Explain how electricity is used in electric heaters and geysers.
Answer:
Electrical energy is
converted into heat
using high-resistance wires (like nichrome).
Why do overhead power cables sag in summer?
Answer:
Metals
expand
due to heat, increasing the length of the wire, causing sagging.
Why should a fuse be connected in the live wire of an electric circuit?
Answer:
A fuse
cuts off current
in case of overloading and prevents damage.
Why are high-voltage transmission lines made of
aluminium
?
Answer:
Aluminium
is
lightweight
and has
low resistivity
, making it a good conductor.
What happens to resistance when resistors are connected in parallel?
Answer:
Total resistance
decreases
and is always
less than the smallest individual resistance
.
Why do electricians wear rubber gloves?
Answer:
Rubber is an
insulator
, preventing electric shock.
Why does a bulb glow immediately when switched on?
Answer:
Electrons move at
high speed
, so current flow is almost instant.
Why is a thick wire used in electric irons?
Answer:
To reduce
resistance
and prevent excessive heating.
How does an electric bell work?
Answer:
Uses
electromagnets
to attract a hammer that strikes the bell repeatedly.
Why is it dangerous to handle electrical appliances with wet hands?
Answer:
Water is a
conductor
, increasing the risk of electric shock.
Why do LED bulbs consume less electricity?
Answer:
LED bulbs
convert most energy into light
, reducing power loss as heat.
