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 50 °C and cools 2 °C each minute at a steady rate. How many minutes until it reaches 26 °C, Bo?

   12 min
2. 2.

   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

3. 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.

4. 3.

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

   • The foam cup, since foam makes heat
   • The glass cup, since you see the cocoa
   • The foam cup with a lid
   • The metal cup, since it is coldest anyway
5. 4.

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

   • The metal cup, since metal is cold
   • The foam cup with a lid
   • Not foam, since foam warms things
   • No cup works for cold drinks
6. 5.

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

   • A foam cup, since foam adds heat
   • A steel bottle with a vacuum layer
   • A plain metal cup, since metal feels cold
   • A paper cup, used once
7. 6.

   Milo says leaving the freezer open lets the cold out. What is a better way to say it?

   • The freezer walls make the cold
   • Heat from the room flows into the freezer
   • The cold escapes into the kitchen
   • Nothing moves; it just looks foggy
8. 7.

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

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

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

   • Radiation and convection
   • Radiation too, since it needs air
   • Just radiation
   • Conduction and convection
10. 9.

    Why does a vacuum bottle also have shiny walls inside, Tala?

    • To reflect radiation, which crosses the vacuum
    • To stop conduction through the air
    • To add warmth to the drink
    • To let cold flow out
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 lets radiation in and stops warm air escaping
    • It lets the cold flow out
    • It blocks radiation, which needs air
    • It makes heat inside the box