Class 10 Household Circuits Mock Test (ICSE)

Topics in Household Circuits

• Transmission of power from the power station
• Ring system and distribution board
• Fuse, MCB and switches
• Earthing and three-pin plug
• Colour coding of wires

Household Circuits practice questions with answers

1. Q1Multiple choice·1 mark
   A safety device used in household electrical circuits that automatically breaks the circuit when excessive current flows due to overloading or short-circuiting is a/an:

   1. (a)step-down transformer
   2. (b)rheostat
   3. (c)earthing wire
   4. (d)electric fuse
   Show answer and step marks

   1. Correct option: (d) electric fuse+1

   Answer: (d)
2. Q2Multiple choice·1 mark
   In the ring main system of domestic wiring, the live, neutral, and earth wires form a continuous loop that originates and terminates at the:

   1. (a)electric meter
   2. (b)main step-down transformer
   3. (c)distribution board
   4. (d)nearest appliance
   Show answer and step marks

   1. Correct option: (c) distribution board+1

   Answer: (c)
3. Q3Multiple choice·1 mark
   According to the modern international colour coding of wires, the colour of the neutral wire is:

   1. (a)Red
   2. (b)Light blue
   3. (c)Black
   4. (d)Green or yellow
   Show answer and step marks

   1. Correct option: (b) Light blue+1

   Answer: (b)
4. Q4Multiple choice·1 mark
   In a three-pin plug, the earth pin is made longer and thicker than the live and neutral pins so that:

   1. (a)it makes earth contact first and breaks it last, and offers least resistance to the operating current.
   2. (b)it completes the live circuit first, and cannot be pushed into the live or neutral hole.
   3. (c)it completes the live circuit first, and offers least resistance to the operating current.
   4. (d)it makes earth contact first and breaks it last, and cannot be pushed into the live or neutral hole.
   Show answer and step marks

   1. Correct option: (d) it makes earth contact first and breaks it last, and cannot be pushed into the live or neutral hole. Being longer, it earths the metal body of the appliance before the live and neutral pins connect and stays connected until they break; being thicker, it cannot be inserted into the narrower live or neutral hole by mistake.+1

   Answer: (d)
5. Q5Long answer·4 marks
   (a) Explain why heavy-power appliances such as geysers and air conditioners are connected to a separate circuit rather than the general lighting circuit in a household wiring system. (b) State two distinct advantages of the ring main system used in domestic wiring over the traditional tree system.
   Show answer and step marks

   1. (a) Heavy-power appliances draw a large current ($I = \frac{P}{V}$), which would overload the thin wires and low-rated fuse of the lighting circuit.+1
   2. (a) A separate power circuit with thicker wires and a higher-rated fuse carries this current without overheating the wiring, so it is safe.+1
   3. (b) First advantage, any one of: the current to any socket reaches it along both paths of the ring, so each part of the cable carries only a share of the load current and a thinner, cheaper cable can be used; extra sockets can be added anywhere along the ring without running a separate line from the distribution board, so less wire is needed; each appliance is protected by its own fuse in its plug, rated to suit that appliance; or any other valid advantage.+1
   4. (b) Second advantage, a different one from the same list.+1

   Answer: (a) Heavy appliances draw a large current that would overheat the thin wiring and blow the fuse of the lighting circuit, so they get a separate circuit with thicker wires and a higher-rated fuse. (b) Any two of: current reaches each socket along two paths, so thinner, cheaper cable can be used; sockets can be added anywhere on the ring with less wiring; each appliance has its own suitably rated fuse in its plug.
6. Q6Long answer·4 marks
   (a) State two distinct advantages of using the ring main system over the tree system in domestic electrical wiring. (b) Explain why all electrical appliances connected via the main distribution board are arranged in parallel across the live and neutral wires rather than in series.
   Show answer and step marks

   1. (a) First advantage, any one of: the current to any socket reaches it along both paths of the ring, so each part of the cable carries only a share of the load current and a thinner, cheaper cable can be used; extra sockets can be added anywhere along the ring without running a separate line from the distribution board, so less wire is needed; each appliance is protected by its own fuse in its plug, rated to suit that appliance; or any other valid advantage.+1
   2. (a) Second advantage, a different one from the same list.+1
   3. (b) Reason for parallel connection: every appliance receives the full mains voltage (e.g. $220\text{ V}$) and draws current according to its own power rating.+1
   4. (b) Consequence of parallel connection: each appliance can be switched on or off independently, and if one is switched off or its circuit breaks (for example a fused bulb), the others continue to work.+1

   Answer: (a) Any two of: current reaches each socket along two paths, so a thinner, cheaper cable can be used; sockets can be added anywhere on the ring with less wiring; each appliance has its own fuse in its plug. (b) In parallel each appliance gets the full mains voltage ($220\text{ V}$) and works independently: switching off or failure (open circuit) of one does not stop the others.

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