WAEC Physics questions: Change of state

11 questions with answers and explanations. Tap an option to check yourself.

1. Question 1· Change of state· WAEC

   The flat part of a cooling curve shows that the substance is

   • Againing heat
   • Bcooling fastest
   • Cat room temperature
   • Dchanging state

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2. Question 2· Change of state· WAEC

   While water is boiling its temperature stays constant because the heat supplied

   • Ais used to overcome the forces between molecules
   • Bescapes to the surroundings
   • Craises the kinetic energy of the molecules
   • Dis changed into light

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3. Question 3· Change of state· WAEC

   How much heat is needed to melt 0.2 kg of ice at 0 °C? [specific latent heat of fusion = 3.36 × 10⁵ J/kg]

   • A6.72 × 10⁴ J
   • B3.36 × 10⁴ J
   • C1.68 × 10⁶ J
   • D6.72 × 10⁵ J

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4. Question 4· Change of state· WAEC

   Boiling differs from evaporation because boiling

   • Atakes place at all temperatures
   • Btakes place at a definite temperature throughout the liquid
   • Coccurs only at the surface
   • Dproduces no vapour

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5. Question 5· Change of state· WAEC

   Food cooks faster in a pressure cooker because

   • Athe pressure lowers the boiling point
   • Bthe higher pressure raises the boiling point of water
   • Csteam escapes quickly
   • Dless heat is needed to melt it

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6. Question 6· Change of state· WAEC

   Evaporation differs from boiling because evaporation

   • Aoccurs throughout the liquid
   • Btakes place only at 100 °C
   • Ctakes place at all temperatures from the surface of the liquid
   • Dneeds no heat

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7. Question 7· Change of state· WAEC

   Heat required to melt 0.5 kg of ice at 0 °C (latent heat 3.4 × 10⁵ J/kg) is

   • A6.8 × 10⁵ J
   • B1.7 × 10⁵ J
   • C3.4 × 10⁵ J
   • D3.4 × 10⁴ J

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   Explanation and discussion

8. Question 8· Change of state· WAEC

   Find the heat needed to change 2 kg of water at 100 °C to steam. (Specific latent heat = 2.26 × 10⁶ J/kg)

   • A4.52 × 10⁶ J
   • B2.26 × 10⁶ J
   • C1.13 × 10⁶ J
   • D9.04 × 10⁶ J

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   Explanation and discussion

9. Question 9· Change of state· WAEC

   The heat absorbed when a solid changes to a liquid without a change in temperature is called

   • Alatent heat of vaporisation
   • Blatent heat of fusion
   • Cspecific heat capacity
   • Dheat of combustion

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10. Question 10· Change of state· WAEC

    The change of a substance directly from solid to vapour is called

    • Acondensation
    • Bevaporation
    • Csublimation
    • Dmelting

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11. Question 11· Change of state· WAEC

    Evaporation differs from boiling in that evaporation

    • Aoccurs at all temperatures from the surface
    • Boccurs at a fixed temperature
    • Cproduces bubbles
    • Dneeds no heat

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    Explanation and discussion