Local action

Back to: PRIMARY SEVEN P7 SCIENCE TOPICAL QUESTIONS AND ANSWERS

Local action
Qn. What is local action?

• Local action is when hydrogen bubbles are seen coming off from the zinc plate.
  Qn. Identify the disadvantages of using wet cells.
• Simple cell produce electricity for a short time.
• Simple cells are bulky (not easily carried).
• Simple cells are only used in an upright position.
  b) Secondary cells
  Qn. What are secondary cells?
• Secondary cells are cells that can be recharged once used up.
  Note:
• Recharging is the process of replacing lost energy in a cell.
  Qn. Give the examples of secondary cells.
• Car batteries / lead acid batteries / accumulates.
• Phone batteries / mobile phone batteries.
  Qn. State the advantages of using secondary cells.
• Secondary cells can be recharged.
• Secondary cells have a high voltage.
• Secondary cells can be used in running heavy / strong machines.
  Qn. State the disadvantages of using secondary cells.
• Secondary cells are expensive.
• Secondary cells are bulky.
• Secondary cells are not easy to maintain.
  A car battery

Qn. State the energy change that takes place in a bulb?

• Electric energy is converted to heat and light energy.
  Qn. State the function of each part of a bulb.
  a) Glass envelope
• The glass envelope protects the inside parts of the bulb.
• The glass envelope prevents nitrogen and organ gases from escaping.
  Note:
  The glass envelope is transparent.
  Qn. Why is the glass envelope transparent?
• To allow light to pass through.
  Qn. Why is argon and nitrogen used in bulbs?
• To prevent evaporation of tungsten.
• To prevent oxygen from mixing with the coiled filament.
• To enable the filament burn at a high temperature with out blowing.
  Note:
• Oxygen cannot be used in an electric bulb because it leads to melting and blowing of the filament.
  b) Brass cap
• The brass cap enables the bulb to be fixed properly in the lamp holder.
  c) Coiled filament
• The coiled filament produces light.
  Qn. Why is the filament coiled?
• To increase electric resistance.
  Qn. From which metal is a coiled filament made? • Tungsten
  Qn. Why is the coiled filament made of tungsten?
• Tungsten has a high melting point.
  Qn. Name the mineral from which tungsten is made?
• Wolfram
  d) Supporting glass stem and filament support.
• The supporting glass stem and filament support hold the filament in position.
  g) Lead wire
• Lead wires conduct electricity from the contact to the filament.
  h) Sealing tube
• The sealing tube enables air to be removed from the bulb.
  i) Contacts
• The contacts transmit electricity from the lamp holder to the bulb.
  OR
• The contacts connect the bulb to the source of electricity from the lamp holder.
  j) Cement
• The cement provides support to the inside parts of the bulb.