The initial number of atoms in a sample is 5.12 × 10²⁰. If the half-life of the sample is 3.0 seconds, determine the number of...

The initial number of atoms in a sample is 5.12 × 10²⁰. If the half-life of the sample is 3.0 seconds, determine the number of atoms that will have decayed after six seconds.

---

After the first half-life, then ½ (5.12 × 10²⁰) = 2.56 × 10²⁰ will have decayed.
The second half-life, then ½ (2.56 × 10²⁰) = 1.28 × 10²⁰ will have decayed.
The total number of decayed atoms = (2.56 + 1.28) × 10²⁰ = 3.84 × 10²⁰ atoms.

---

Mutiso answered the question on October 17, 2018 at 10:10

Exams With Marking Schemes

• Grade 1
• Grade 2
• Grade 3
• Grade 4
• Grade 5
• Grade 6
• Grade 7
• Grade 8
• Grade 9
• PP1
• PP2
• Playgroup
• Form 1
• Form 2
• Form 3
• Form 4

Related Questions

---

• The half-life of a sample of a radioactive substance is 98 minutes. How long does it take for the activity of the sample to reduce... (Solved)
  

  The half-life of a sample of a radioactive substance is 98 minutes. How long does it take for the activity of the sample to reduce to 1/16^th of the original value?

  Date posted: October 17, 2018 .    Answers (1)

• Explain ways of detecting nuclear radiation (Solved)
  

  Explain ways of detecting nuclear radiation.

  Date posted: October 17, 2018 .    Answers (1)

• Sodium has a work function of 2.0 e: Calculate (a) The maximum energy and velocity of the emitted electrons when sodium is Illuminated by... (Solved)
  

  Sodium has a work function of 2.0 e: Calculate
  (a) The maximum energy and velocity of the emitted electrons when sodium is Illuminated by a radiation of wavelength 150 nm.
  (b) Determine the least frequency of radiation by which electrons are emitted. (Take ‘h’ = 6.626 × 10-34 Js, e = 1.6 × 10-19, c = 3.0 × 108 m/s and mass of electron = 9.1 × 10-31 kg).

  Date posted: October 17, 2018 .    Answers (1)

• The threshold frequency for lithium is 5.5 × 10¹⁴ Hz. Calculate the work function for lithium. (Take ‘h’ = 6.626 × 10^-34 Js) (Solved)
  

  The threshold frequency for lithium is 5.5 × 10¹⁴ Hz. Calculate the work function for lithium. (Take ‘h’ = 6.626 × 10^-34 Js)

  Date posted: October 17, 2018 .    Answers (1)

• Cathode Ray Oscilloscope components and functioning (Solved)
  

  Cathode Ray Oscilloscope components and functioning.

  Date posted: October 16, 2018 .    Answers (1)

• Illustrate domestic wiring system with aid of a diagram (Solved)
  

  Illustrate domestic wiring system with aid of a diagram

  Date posted: October 16, 2018 .    Answers (1)

• A house has five rooms each with a 60 W, 240 V bulb. If the bulbs are switched on from 7.00 pm to 10.30 pm,... (Solved)
  

  A house has five rooms each with a 60 W, 240 V bulb. If the bulbs are switched on from 7.00 pm to 10.30 pm, calculate the;
  (a) Power consumed per day in kWh
  (b) Cost per week for lighting those rooms if it costs 90 cents per unit.

  Date posted: October 16, 2018 .    Answers (1)

• An electric kettle is rated at 2,500 W and uses a voltage of 240 V. (a) If electricity costs Ksh 1.10 per kWh, what is... (Solved)
  

  An electric kettle is rated at 2,500 W and uses a voltage of 240 V. (a) If electricity costs Ksh 1.10 per kWh, what is the cost of running it for 6 hrs? (b) What would be its rate of dissipating energy if the mains voltage was dropped to 120 V?

  Date posted: October 16, 2018 .    Answers (1)

• Briefly explain the process of power generation and transmission (Solved)
  

  Explain the process of power transmission

  Date posted: October 16, 2018 .    Answers (1)

• A step-up transformer has 10,000 turns in the secondary coil and 100 turns in the primary coil. An alternating current of 0.5 A flows in... (Solved)
  

  A step-up transformer has 10,000 turns in the secondary coil and 100 turns in the primary coil. An alternating current of 0.5 A flows in the primary circuit when connected to a 12.0 V a.c. supply.
  (a) Calculate the voltage across the secondary coil (b) If the transformer has an efficiency of 90%, what is the current in the secondary coil?

  Date posted: October 16, 2018 .    Answers (1)

• A current of 0.6 A is passed through a step up transformer with a primary coil of 200 turns and a current of 0.1 A... (Solved)
  

  A current of 0.6 A is passed through a step up transformer with a primary coil of 200 turns and a current of 0.1 A is obtained in the secondary coil. Determine the number of turns in the secondary coil and the voltage across if the primary coil is connected to a 240 V mains.

  Date posted: October 16, 2018 .    Answers (1)

• A material of density 8.5 gcm^-3 is attached to a piece of wood of mass 100g and density 0.2 gcm^-3. Calculate the volume of material... (Solved)
  

  A material of density 8.5 gcm^-3 is attached to a piece of wood of mass 100g and density 0.2 gcm^-3. Calculate the volume of material X which must be attached to the piece of wood so that the two just submerge beneath a liquid of density 1.2 gcm^-3.

  Date posted: October 16, 2018 .    Answers (1)

• A balloon made up of a fabric weighing 80 N has a volume of 1.0 × 10⁷ cm. the balloon is filled with hydrogen of... (Solved)
  

  A balloon made up of a fabric weighing 80 N has a volume of 1.0 × 10⁷ cm. the balloon is filled with hydrogen of density 0.9 kgm^-3. Calculate the greatest weight in addition to that of the hydrogen and the fabric, which the balloon can carry in air of average density 1.25 kgm^-3

  Date posted: October 16, 2018 .    Answers (1)

• A solid of mass 1.0 kg is suspended using a thread and then submerged in water. If the tension on the thread is 5.0 N,... (Solved)
  

  A solid of mass 1.0 kg is suspended using a thread and then submerged in water. If the tension on the thread is 5.0 N, determine the relative density of the solid.

  Date posted: October 16, 2018 .    Answers (1)

• Describe experiment to determine the relative density of a cork (Solved)
  

  Describe experiment to determine the relative density of a cork

  Date posted: October 16, 2018 .    Answers (1)

• A wooden block of dimensions 3 cm × 3 cm × 4 cm floats vertically in methylated spirit with 4 cm of its length in... (Solved)
  

  A wooden block of dimensions 3 cm × 3 cm × 4 cm floats vertically in methylated spirit with 4 cm of its length in the spirit. Calculate the weight of the block. (Density of methylated spirit = 8.0 × 10² kgm^-3)

  Date posted: October 16, 2018 .    Answers (1)

• Describe experiment to demonstrate the law of flotation (Solved)
  

  Describe experiment to demonstrate the law of flotation

  Date posted: October 16, 2018 .    Answers (1)

• A block of metal of volume 60 cm³ weighs 4.80 N in air. Determine its weight when fully submerged in a liquid of density 1,200... (Solved)
  

  A block of metal of volume 60 cm³ weighs 4.80 N in air. Determine its weight when fully submerged in a liquid of density 1,200 kgm^-3.

  Date posted: October 16, 2018 .    Answers (1)

• Describe an experiment to demonstrate Archimedes principle (Solved)
  

  Describe an experiment to demonstrate Archimedes principle

  Date posted: October 16, 2018 .    Answers (1)

• Explain the common eye defects and their corrections (Solved)
  

  Explain the common eye defects and their corrections.

  Date posted: October 15, 2018 .    Answers (1)