Conduction, convection and radiation

Answer Key - Grade 8 Science Worksheet - Challenge Me

Circle the best answer, or write your answer on the line.

1. 1.

   A teacher's water is at 70 °C and cools 3 °C each minute at a steady rate. How many minutes until it reaches 40 °C, Ari?

   10 min
2. 2.

   A teacher's water is at 50 °C and cools 2 °C each minute at a steady rate. How many minutes until it reaches 26 °C, Bo?

   12 min
3. 3.

   A teacher's water is at 90 °C and cools 4 °C each minute at a steady rate. How many minutes until it reaches 54 °C, Esme?

   9 min

4. Read this first

   Use this

   Investigation card (test results). A teacher pours the same warm water (60 °C) into three cups and waits 20 minutes. Foam cup with lid: dropped 6 °C. Glass cup: dropped 15 °C. Metal cup: dropped 22 °C.

5. 4.

   Jun wants to keep cocoa warm on a field trip. Using the test, which cup is best?

   • The glass cup, since you see the cocoa
   • The foam cup with a lid
   • The metal cup, since it is coldest anyway
   • The foam cup, since foam makes heat
6. 5.

   Now Kira wants to keep lemonade cold. Using the same test, which cup is best?

   • The metal cup, since metal is cold
   • Not foam, since foam warms things
   • No cup works for cold drinks
   • The foam cup with a lid
7. 6.

   Luz wants a cup that keeps drinks warm and can be reused for years. Which choice balances both best?

   • A paper cup, used once
   • A steel bottle with a vacuum layer
   • A plain metal cup, since metal feels cold
   • A foam cup, since foam adds heat
8. 7.

   Noah says a winter coat keeps you warm because it makes heat. Agree or disagree?

   • Disagree: it slows your heat from leaving
   • Disagree: coats do nothing
   • Agree: thick coats make heat
   • Agree: it blocks the cold from getting in to your body
9. 8.

   Pia says ice cools a drink by giving its cold to the drink. Agree or disagree?

   • Disagree: the drink's heat flows into the ice
   • Agree: cold sinks into the drink
   • Agree: the ice's cold spreads out into the drink
   • Disagree: ice doesn't cool drinks
10. 9.

    A vacuum bottle has an empty space between two walls. Which paths does the empty space stop, Ren?

    • Radiation and convection
    • Conduction and convection
    • Just radiation
    • Radiation too, since it needs air
11. 10.

    Zee's class reads about a solar oven: a dark box with a clear plastic lid in the sun. What does the lid do?

    • It makes heat inside the box
    • It lets radiation in and stops warm air escaping
    • It blocks radiation, which needs air
    • It lets the cold flow out