RBSE Class 10 Science Solutions Chapter 12 Electricity

RBSE Class 10 Science Solutions Chapter 12 Electricity

RBSE Class 10 Science Chapter 12 Electricity InText Questions and Answers

Page 200.

Question 1.
What does an electric circuit mean?
Answer:
An electric circuit consists of closed path in which different components like cells, ammeter, voltmeter, resistance etc. are attached.

Page 202.

Question 1.
Name a device that helps to maintain a potential difference across a conductor.
Answer:
A cell or battery helps to maintain a potential difference across conductor.

Page 209.

Question 1.
On what factors does the resistance of a conductor depend?
Answer:
Resistance of a conductor depends on (i) length, (ii) area of cross section, (iii) nature of material, (iv) temperature.

Question 2.
Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?
Answer:
As we know that resistance produces obstruction in the path of current which is inversely proportional to the area of cross – section of the conductor (R α 1/A) So a thick conductor offers lesser resistance than a thin wire.

Question 3.
Let the resistance of an electrical component remains constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?
Answer:
According to Ohm’s law, V α I. As the value of potential difference decreases to half of its former value, the value of current also changes to half of former value.

Question 4.
Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
Answer:
Generally coils of electric toasters and electric irons are made of nichrome. Nichrome is an alloy of nickel (60%), chromium (12%), manganese (2%) and iron (26%). The use of this metal is because

1. Resistivity of an alloy is generally higher than that of pure metal.
2. They have high melting point.
3. On heating ( 800°C), they does not oxidise easily.

Question 5.
Use the data in Table 12.2 to answer the following questions:
(a) Which among iron and mercury is a better conductor?
(b) Which material is the best conductor?
Answer:
(a) Iron is a better conductor as it has low resistivity.
(b) Silver is the best conductor.

Page 213.

Page 216.

Question 1.
Judge the equivalent resistance when the following are connected in parallel: (a) 1Ω and 10⁶Ω, (b) 1Ω. and 10³Ω, and 10⁶Ω.
Answer:

Question 2.
An electric lamp of 100Ω, a toaster of resistance 50Ω, and a water filter of resistance 500Ω. are connected in parallel to a 220V source. What is the resistance of an electric iron connected to the same sources that takes as much current as all three appliances, and what is the current through it?
Answer:
In parallel combination resistance of electric iron will be equal to the resultant of these three appliances connected in parallel.

Question 3.
What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?
Answer:
1. In parallel combination the potential difference across each device remains the same where as in series connections it is distributed.
2. If any appliance is switched ‘ON’ or ‘OFF’ it does not affect the working of other devices.

Question 4.
How can three resistors of resistances 2Ω, 3Ω, and 6Ω be connected to give a total resistance of (a) 4Ω, (b) 1Ω?
Answer:
(a) To get a total resistance of 4Ω from three resistors 2Ω, 3Ω and 6Ω, then resistors 3Ω and 6Ω should be connected in parallel with 2Ω in series with them.

Page 218.

Question 1.
Why does the cord of an electric heater not glow while the heating element.
Answer:
The coil of the electric heater is made of alloy nichrome. The resistivity of nichrome is very high. So when the current is flowing, the heating element glow. While the cord of the electric heater is made of copper or aluminium, the resistance of which is very low so it does not glow.

Question 3.
An electric iron of resistance 20Ω takes a current of 5A. Calculate the heat developed in 30s.
Answer:
Given
R = 20Ω
I = 5A
t = 30s
By H = I²Rt
= (5)² x 20 x 30 = 15000 Joule
Hence H = 1.5 x 10⁴ Joule

Page 220.

Question 1.
What determines the rate at which energy is delivered by a current?
Answer:
Electric power determines the rate at which energy is delivered by a current.

Question 2.
An electric motor takes 5A from a 220V line. Determine the power of the motor and the energy consumed in 2h.
Answer:
Given
I = 5A
V = 220V
as, P = VI
= 220 x 5A = 1100 W
Energy consumed in 2 hours
= 1100W x 2h
= 2200Wh
= 2200Watt x 60 x 60 secs.
= 7920000 Joule = 7.92 x 10⁶ Joule.

RBSE Class 10 Science Chapter 12 Electricity Textbook Questions and Answers

Question 1.
A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R’ then the ratio R/R’ is.
(a) 1/25
(b) 1/5
(c) 5
(d) 25
Answer:
(d) 25

Question 2.
Which of the following terms does not represent electrical power in a circuit?
(a) I²R
(b) IR²
(c) VI
(d) V²/R
Answer:
(b) IR²

Question 3.
An electric bulb is rated 220V and 100W. When it is operated on 110V, the power consumed will be.
(a) 100W
(b) 70W
(c) 50W
(d) 25W
Answer:
(d) 25W

Question 4.
Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be.
(a) 1 : 2
(b) 2 : 1
(c) 1 : 4
(d) 4 : 1
Answer:
(c) 1 : 4

Question 5.
How is a voltmeter connected in the circuit to measure the potential difference between two points?
Answer:
A voltmeter is always connected parallel in the circuit to measure the potential difference between two points.

Question 7.
The values of current flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below.

Plot a graph between V and I and calculate the resistance of that resistor.
Answer:
The resistance of the resistor will be equal to the slope of the graph.

Question 16.
Which uses more energy, a 250W TV set in 1hr, or a 1200W toaster in 10 minutes?
Answer:
Given
For TV P₁ = 250W
t₁ = 1 hour = 60 x 60 sec
t₁ = 3600 sec
Energy consumed
H₁ = P₁ x t₁ = 250W x 3600 s
= 900000J
= 9 x 105J
For toaster
P₂ = 12W
t₂ = 10 min
= 600s
∴ Energy consumed
H₂ = P₂ x t₂ = 120 x 600
= 72000J
= 7.2 x 104J
Here it is clear that H₁> H₂
Therefore, the TV set consumed more energy.

Question 17.
An electric heater of resistance 8Ω draws 15A from the service mains 2 hours. Calculate the rate at which heat is developed in the heater.
Answer:
Given, R = 8Ω, I = 15A, t = 2hr
Rate at which heat is developed H = P = I₂
R = 15 x 8 = 1800W or 1800J/s

Question 18.
Explain the following

1. Why is the tungsten used almost exclusively for filament of electric lamps?
2. Why are the conductors of electric heating devices, such as bread – toasters and electric irons, made of an alloy rather than a pure metal?
3. Why is the series arrangement not used for domestic circuits?
4. How does the resistance of a wire vary with its area of cross – section?
5.  Why are copper and aluminium wires usually employed for electricity transmission

Answer:

1. Due to high melting point of tungsten ( 3380° ), it becomes incandescent at 2400K.
2. The resistivity of alloys are generally higher than that of pure metals of which they are made of.
3. In series circuits, same current flows then if any one of the electric appliance fails or in off position, then all the other appliances stop working because same electric current is flowing through all of them.
4. The resistace of a wire (R) varies inversely as its cross – sectional area (A) i.e., R α 1/A
5. Due to very low resistivity, copper and aluminium wires are generally used for electricity transmission.