Practice Nuclear Fusion in Physics

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

Nuclear fusion is the joining of light nuclei to form a heavier nucleus, releasing energy if the final nucleus is more tightly bound.

Small nuclei can combine and release energy, especially inside stars.

Showing a random 20 of 50 problems.

Example 1

easy
If 4.5×10−12 J4.5\times10^{-12}\text{ J} is released per fusion, how many joules come from 2×10152\times10^{15} fusions?

Example 2

easy
In fusion, is the product nucleus's mass slightly more or less than the sum of the original nuclei?

Example 3

medium
The Sun converts about 4×109 kg4\times10^9 \text{ kg} of mass to energy per second. Find the power output (c=3×108c = 3\times10^8).

Example 4

easy
In a deuterium-tritium fusion, the products are a helium-4 nucleus and a ___.

Example 5

easy
Which reaction joins nuclei: fusion or fission?

Example 6

medium
A fusion mass defect is 0.7%0.7\% of the reactant mass 1×10−26 kg1\times10^{-26} \text{ kg}. Find the energy released (c=3×108c = 3\times10^8).

Example 7

medium
The deuteron has mass 3.34358×10−27 kg3.34358\times10^{-27}\text{ kg}; two protons have combined mass 3.34754×10−27 kg3.34754\times10^{-27}\text{ kg} (ignoring positron/neutrino subtleties). Estimate the mass defect for forming a deuteron.

Example 8

medium
Compare 1 kg1\text{ kg} of fusion fuel (∼0.4%\sim 0.4\% mass-to-energy) with 1 kg1\text{ kg} of gasoline (∼4.7×107 J\sim 4.7\times10^7\text{ J}). How many times more energy does fusion give? (c=3×108c=3\times10^8)

Example 9

hard
The triple product n T τEn\,T\,\tau_E that quantifies fusion-plasma confinement is named the ___ criterion.

Example 10

easy
The hot, ionized gas state in which fusion takes place in stars is called a ___.

Example 11

hard
The Sun has ∼1.4×1030 kg\sim 1.4\times10^{30}\text{ kg} of hydrogen-rich core fuel and converts about 0.7%0.7\% to energy. Estimate the total fusion energy reserve. (c=3×108c=3\times10^8)

Example 12

medium
The condition that fusion power produced equals the power needed to sustain the plasma is called ___.

Example 13

easy
Why is fusion hard to achieve on Earth?

Example 14

medium
The Sun loses about 4.3×109 kg/s4.3\times10^9\text{ kg/s} to fusion. Over 11 year (3.15×107 s3.15\times10^7\text{ s}), find the mass converted.

Example 15

easy
Nuclear fusion is the joining of what kind of nuclei?

Example 16

medium
Why do two positively charged nuclei need high speed (temperature) to fuse?

Example 17

medium
A D-T reaction releases 17.6 MeV17.6\text{ MeV}. If 80%80\% of this is carried by the neutron, find the neutron's kinetic energy in joules. (1 MeV=1.6×10−13 J1\text{ MeV}=1.6\times10^{-13}\text{ J})

Example 18

medium
A fusion reaction has mass defect 5×10−29 kg5\times10^{-29} \text{ kg}. Find the energy released (c=3×108c = 3\times10^8).

Example 19

hard
Each pp-chain cycle releases 4.27×10−12 J4.27\times10^{-12}\text{ J}. If the Sun's luminosity is 3.85×1026 W3.85\times10^{26}\text{ W}, find the number of cycles per second.

Example 20

challenge
Fusion of 1 kg1 \text{ kg} of hydrogen converts about 0.7%0.7\% of its mass to energy. Find that energy (c=3×108c = 3\times10^8).
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