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9
2139-2142
The scattered alpha-particles on striking the screen produced brief light flashes or scintillations These flashes may be viewed through a microscope and the distribution of the number of scattered particles may be studied as a function of angle of scattering FIGURE 12 2 Schematic arrangement of the Geiger-Marsden experiment
9
2140-2143
These flashes may be viewed through a microscope and the distribution of the number of scattered particles may be studied as a function of angle of scattering FIGURE 12 2 Schematic arrangement of the Geiger-Marsden experiment A typical graph of the total number of a-particles scattered at different angles, in a given interval of time, is shown in Fig
9
2141-2144
FIGURE 12 2 Schematic arrangement of the Geiger-Marsden experiment A typical graph of the total number of a-particles scattered at different angles, in a given interval of time, is shown in Fig 12
9
2142-2145
2 Schematic arrangement of the Geiger-Marsden experiment A typical graph of the total number of a-particles scattered at different angles, in a given interval of time, is shown in Fig 12 3
9
2143-2146
A typical graph of the total number of a-particles scattered at different angles, in a given interval of time, is shown in Fig 12 3 The dots in this figure represent the data points and the solid curve is the theoretical prediction based on the assumption that the target atom has a small, dense, positively charged nucleus
9
2144-2147
12 3 The dots in this figure represent the data points and the solid curve is the theoretical prediction based on the assumption that the target atom has a small, dense, positively charged nucleus Many of the a-particles pass through the foil
9
2145-2148
3 The dots in this figure represent the data points and the solid curve is the theoretical prediction based on the assumption that the target atom has a small, dense, positively charged nucleus Many of the a-particles pass through the foil It means that they do not suffer any collisions
9
2146-2149
The dots in this figure represent the data points and the solid curve is the theoretical prediction based on the assumption that the target atom has a small, dense, positively charged nucleus Many of the a-particles pass through the foil It means that they do not suffer any collisions Only about 0
9
2147-2150
Many of the a-particles pass through the foil It means that they do not suffer any collisions Only about 0 14% of the incident a-particles scatter by more than 1°; and about 1 in 8000 deflect by more than 90°
9
2148-2151
It means that they do not suffer any collisions Only about 0 14% of the incident a-particles scatter by more than 1°; and about 1 in 8000 deflect by more than 90° Rutherford argued that, to deflect the a-particle backwards, it must experience a large repulsive force
9
2149-2152
Only about 0 14% of the incident a-particles scatter by more than 1°; and about 1 in 8000 deflect by more than 90° Rutherford argued that, to deflect the a-particle backwards, it must experience a large repulsive force This force could FIGURE 12
9
2150-2153
14% of the incident a-particles scatter by more than 1°; and about 1 in 8000 deflect by more than 90° Rutherford argued that, to deflect the a-particle backwards, it must experience a large repulsive force This force could FIGURE 12 1 Geiger-Marsden scattering experiment
9
2151-2154
Rutherford argued that, to deflect the a-particle backwards, it must experience a large repulsive force This force could FIGURE 12 1 Geiger-Marsden scattering experiment The entire apparatus is placed in a vacuum chamber (not shown in this figure)
9
2152-2155
This force could FIGURE 12 1 Geiger-Marsden scattering experiment The entire apparatus is placed in a vacuum chamber (not shown in this figure) Rationalised 2023-24 293 Atoms be provided if the greater part of the mass of the atom and its positive charge were concentrated tightly at its centre
9
2153-2156
1 Geiger-Marsden scattering experiment The entire apparatus is placed in a vacuum chamber (not shown in this figure) Rationalised 2023-24 293 Atoms be provided if the greater part of the mass of the atom and its positive charge were concentrated tightly at its centre Then the incoming a-particle could get very close to the positive charge without penetrating it, and such a close encounter would result in a large deflection
9
2154-2157
The entire apparatus is placed in a vacuum chamber (not shown in this figure) Rationalised 2023-24 293 Atoms be provided if the greater part of the mass of the atom and its positive charge were concentrated tightly at its centre Then the incoming a-particle could get very close to the positive charge without penetrating it, and such a close encounter would result in a large deflection This agreement supported the hypothesis of the nuclear atom
9
2155-2158
Rationalised 2023-24 293 Atoms be provided if the greater part of the mass of the atom and its positive charge were concentrated tightly at its centre Then the incoming a-particle could get very close to the positive charge without penetrating it, and such a close encounter would result in a large deflection This agreement supported the hypothesis of the nuclear atom This is why Rutherford is credited with the discovery of the nucleus
9
2156-2159
Then the incoming a-particle could get very close to the positive charge without penetrating it, and such a close encounter would result in a large deflection This agreement supported the hypothesis of the nuclear atom This is why Rutherford is credited with the discovery of the nucleus In Rutherford’s nuclear model of the atom, the entire positive charge and most of the mass of the atom are concentrated in the nucleus with the electrons some distance away
9
2157-2160
This agreement supported the hypothesis of the nuclear atom This is why Rutherford is credited with the discovery of the nucleus In Rutherford’s nuclear model of the atom, the entire positive charge and most of the mass of the atom are concentrated in the nucleus with the electrons some distance away The electrons would be moving in orbits about the nucleus just as the planets do around the sun
9
2158-2161
This is why Rutherford is credited with the discovery of the nucleus In Rutherford’s nuclear model of the atom, the entire positive charge and most of the mass of the atom are concentrated in the nucleus with the electrons some distance away The electrons would be moving in orbits about the nucleus just as the planets do around the sun Rutherford’s experiments suggested the size of the nucleus to be about 10–15 m to 10–14 m
9
2159-2162
In Rutherford’s nuclear model of the atom, the entire positive charge and most of the mass of the atom are concentrated in the nucleus with the electrons some distance away The electrons would be moving in orbits about the nucleus just as the planets do around the sun Rutherford’s experiments suggested the size of the nucleus to be about 10–15 m to 10–14 m From kinetic theory, the size of an atom was known to be 10–10 m, about 10,000 to 100,000 times larger than the size of the nucleus (see Chapter 10, Section 10
9
2160-2163
The electrons would be moving in orbits about the nucleus just as the planets do around the sun Rutherford’s experiments suggested the size of the nucleus to be about 10–15 m to 10–14 m From kinetic theory, the size of an atom was known to be 10–10 m, about 10,000 to 100,000 times larger than the size of the nucleus (see Chapter 10, Section 10 6 in Class XI Physics textbook)
9
2161-2164
Rutherford’s experiments suggested the size of the nucleus to be about 10–15 m to 10–14 m From kinetic theory, the size of an atom was known to be 10–10 m, about 10,000 to 100,000 times larger than the size of the nucleus (see Chapter 10, Section 10 6 in Class XI Physics textbook) Thus, the electrons would seem to be at a distance from the nucleus of about 10,000 to 100,000 times the size of the nucleus itself
9
2162-2165
From kinetic theory, the size of an atom was known to be 10–10 m, about 10,000 to 100,000 times larger than the size of the nucleus (see Chapter 10, Section 10 6 in Class XI Physics textbook) Thus, the electrons would seem to be at a distance from the nucleus of about 10,000 to 100,000 times the size of the nucleus itself Thus, most of an atom is empty space
9
2163-2166
6 in Class XI Physics textbook) Thus, the electrons would seem to be at a distance from the nucleus of about 10,000 to 100,000 times the size of the nucleus itself Thus, most of an atom is empty space With the atom being largely empty space, it is easy to see why most a-particles go right through a thin metal foil
9
2164-2167
Thus, the electrons would seem to be at a distance from the nucleus of about 10,000 to 100,000 times the size of the nucleus itself Thus, most of an atom is empty space With the atom being largely empty space, it is easy to see why most a-particles go right through a thin metal foil However, when a-particle happens to come near a nucleus, the intense electric field there scatters it through a large angle
9
2165-2168
Thus, most of an atom is empty space With the atom being largely empty space, it is easy to see why most a-particles go right through a thin metal foil However, when a-particle happens to come near a nucleus, the intense electric field there scatters it through a large angle The atomic electrons, being so light, do not appreciably affect the a-particles
9
2166-2169
With the atom being largely empty space, it is easy to see why most a-particles go right through a thin metal foil However, when a-particle happens to come near a nucleus, the intense electric field there scatters it through a large angle The atomic electrons, being so light, do not appreciably affect the a-particles The scattering data shown in Fig
9
2167-2170
However, when a-particle happens to come near a nucleus, the intense electric field there scatters it through a large angle The atomic electrons, being so light, do not appreciably affect the a-particles The scattering data shown in Fig 12
9
2168-2171
The atomic electrons, being so light, do not appreciably affect the a-particles The scattering data shown in Fig 12 3 can be analysed by employing Rutherford’s nuclear model of the atom
9
2169-2172
The scattering data shown in Fig 12 3 can be analysed by employing Rutherford’s nuclear model of the atom As the gold foil is very thin, it can be assumed that a-particles will suffer not more than one scattering during their passage through it
9
2170-2173
12 3 can be analysed by employing Rutherford’s nuclear model of the atom As the gold foil is very thin, it can be assumed that a-particles will suffer not more than one scattering during their passage through it Therefore, computation of the trajectory of an alpha-particle scattered by a single nucleus is enough
9
2171-2174
3 can be analysed by employing Rutherford’s nuclear model of the atom As the gold foil is very thin, it can be assumed that a-particles will suffer not more than one scattering during their passage through it Therefore, computation of the trajectory of an alpha-particle scattered by a single nucleus is enough Alpha- particles are nuclei of helium atoms and, therefore, carry two units, 2e, of positive charge and have the mass of the helium atom
9
2172-2175
As the gold foil is very thin, it can be assumed that a-particles will suffer not more than one scattering during their passage through it Therefore, computation of the trajectory of an alpha-particle scattered by a single nucleus is enough Alpha- particles are nuclei of helium atoms and, therefore, carry two units, 2e, of positive charge and have the mass of the helium atom The charge of the gold nucleus is Ze, where Z is the atomic number of the atom; for gold Z = 79
9
2173-2176
Therefore, computation of the trajectory of an alpha-particle scattered by a single nucleus is enough Alpha- particles are nuclei of helium atoms and, therefore, carry two units, 2e, of positive charge and have the mass of the helium atom The charge of the gold nucleus is Ze, where Z is the atomic number of the atom; for gold Z = 79 Since the nucleus of gold is about 50 times heavier than an a-particle, it is reasonable to assume that it remains stationary throughout the scattering process
9
2174-2177
Alpha- particles are nuclei of helium atoms and, therefore, carry two units, 2e, of positive charge and have the mass of the helium atom The charge of the gold nucleus is Ze, where Z is the atomic number of the atom; for gold Z = 79 Since the nucleus of gold is about 50 times heavier than an a-particle, it is reasonable to assume that it remains stationary throughout the scattering process Under these assumptions, the trajectory of an alpha-particle can be computed employing Newton’s second law of motion and the Coulomb’s law for electrostatic force of repulsion between the alpha-particle and the positively charged nucleus
9
2175-2178
The charge of the gold nucleus is Ze, where Z is the atomic number of the atom; for gold Z = 79 Since the nucleus of gold is about 50 times heavier than an a-particle, it is reasonable to assume that it remains stationary throughout the scattering process Under these assumptions, the trajectory of an alpha-particle can be computed employing Newton’s second law of motion and the Coulomb’s law for electrostatic force of repulsion between the alpha-particle and the positively charged nucleus FIGURE 12
9
2176-2179
Since the nucleus of gold is about 50 times heavier than an a-particle, it is reasonable to assume that it remains stationary throughout the scattering process Under these assumptions, the trajectory of an alpha-particle can be computed employing Newton’s second law of motion and the Coulomb’s law for electrostatic force of repulsion between the alpha-particle and the positively charged nucleus FIGURE 12 3 Experimental data points (shown by dots) on scattering of a-particles by a thin foil at different angles obtained by Geiger and Marsden using the setup shown in Figs
9
2177-2180
Under these assumptions, the trajectory of an alpha-particle can be computed employing Newton’s second law of motion and the Coulomb’s law for electrostatic force of repulsion between the alpha-particle and the positively charged nucleus FIGURE 12 3 Experimental data points (shown by dots) on scattering of a-particles by a thin foil at different angles obtained by Geiger and Marsden using the setup shown in Figs 12
9
2178-2181
FIGURE 12 3 Experimental data points (shown by dots) on scattering of a-particles by a thin foil at different angles obtained by Geiger and Marsden using the setup shown in Figs 12 1 and 12
9
2179-2182
3 Experimental data points (shown by dots) on scattering of a-particles by a thin foil at different angles obtained by Geiger and Marsden using the setup shown in Figs 12 1 and 12 2
9
2180-2183
12 1 and 12 2 Rutherford’s nuclear model predicts the solid curve which is seen to be in good agreement with experiment
9
2181-2184
1 and 12 2 Rutherford’s nuclear model predicts the solid curve which is seen to be in good agreement with experiment Rationalised 2023-24 Physics 294 EXAMPLE 12
9
2182-2185
2 Rutherford’s nuclear model predicts the solid curve which is seen to be in good agreement with experiment Rationalised 2023-24 Physics 294 EXAMPLE 12 1 The magnitude of this force is 2 0 (2 )( ) 1 4 e Ze F r ε = π (12
9
2183-2186
Rutherford’s nuclear model predicts the solid curve which is seen to be in good agreement with experiment Rationalised 2023-24 Physics 294 EXAMPLE 12 1 The magnitude of this force is 2 0 (2 )( ) 1 4 e Ze F r ε = π (12 1) where r is the distance between the a-particle and the nucleus
9
2184-2187
Rationalised 2023-24 Physics 294 EXAMPLE 12 1 The magnitude of this force is 2 0 (2 )( ) 1 4 e Ze F r ε = π (12 1) where r is the distance between the a-particle and the nucleus The force is directed along the line joining the a-particle and the nucleus
9
2185-2188
1 The magnitude of this force is 2 0 (2 )( ) 1 4 e Ze F r ε = π (12 1) where r is the distance between the a-particle and the nucleus The force is directed along the line joining the a-particle and the nucleus The magnitude and direction of the force on an a-particle continuously changes as it approaches the nucleus and recedes away from it
9
2186-2189
1) where r is the distance between the a-particle and the nucleus The force is directed along the line joining the a-particle and the nucleus The magnitude and direction of the force on an a-particle continuously changes as it approaches the nucleus and recedes away from it 12
9
2187-2190
The force is directed along the line joining the a-particle and the nucleus The magnitude and direction of the force on an a-particle continuously changes as it approaches the nucleus and recedes away from it 12 2
9
2188-2191
The magnitude and direction of the force on an a-particle continuously changes as it approaches the nucleus and recedes away from it 12 2 1 Alpha-particle trajectory The trajectory traced by an a-particle depends on the impact parameter, b of collision
9
2189-2192
12 2 1 Alpha-particle trajectory The trajectory traced by an a-particle depends on the impact parameter, b of collision The impact parameter is the perpendicular distance of the initial velocity vector of the a-particle from the centre of the nucleus (Fig
9
2190-2193
2 1 Alpha-particle trajectory The trajectory traced by an a-particle depends on the impact parameter, b of collision The impact parameter is the perpendicular distance of the initial velocity vector of the a-particle from the centre of the nucleus (Fig 12
9
2191-2194
1 Alpha-particle trajectory The trajectory traced by an a-particle depends on the impact parameter, b of collision The impact parameter is the perpendicular distance of the initial velocity vector of the a-particle from the centre of the nucleus (Fig 12 4)
9
2192-2195
The impact parameter is the perpendicular distance of the initial velocity vector of the a-particle from the centre of the nucleus (Fig 12 4) A given beam of a-particles has a distribution of impact parameters b, so that the beam is scattered in various directions with different probabilities (Fig
9
2193-2196
12 4) A given beam of a-particles has a distribution of impact parameters b, so that the beam is scattered in various directions with different probabilities (Fig 12
9
2194-2197
4) A given beam of a-particles has a distribution of impact parameters b, so that the beam is scattered in various directions with different probabilities (Fig 12 4)
9
2195-2198
A given beam of a-particles has a distribution of impact parameters b, so that the beam is scattered in various directions with different probabilities (Fig 12 4) (In a beam, all particles have nearly same kinetic energy
9
2196-2199
12 4) (In a beam, all particles have nearly same kinetic energy ) It is seen that an a-particle close to the nucleus (small impact parameter) suffers large scattering
9
2197-2200
4) (In a beam, all particles have nearly same kinetic energy ) It is seen that an a-particle close to the nucleus (small impact parameter) suffers large scattering In case of head-on collision, the impact parameter is minimum and the a-particle rebounds back (q @ p)
9
2198-2201
(In a beam, all particles have nearly same kinetic energy ) It is seen that an a-particle close to the nucleus (small impact parameter) suffers large scattering In case of head-on collision, the impact parameter is minimum and the a-particle rebounds back (q @ p) For a large impact parameter, the a-particle goes nearly undeviated and has a small deflection (q @ 0)
9
2199-2202
) It is seen that an a-particle close to the nucleus (small impact parameter) suffers large scattering In case of head-on collision, the impact parameter is minimum and the a-particle rebounds back (q @ p) For a large impact parameter, the a-particle goes nearly undeviated and has a small deflection (q @ 0) The fact that only a small fraction of the number of incident particles rebound back indicates that the number of a-particles undergoing head on collision is small
9
2200-2203
In case of head-on collision, the impact parameter is minimum and the a-particle rebounds back (q @ p) For a large impact parameter, the a-particle goes nearly undeviated and has a small deflection (q @ 0) The fact that only a small fraction of the number of incident particles rebound back indicates that the number of a-particles undergoing head on collision is small This, in turn, implies that the mass and positive charge of the atom is concentrated in a small volume
9
2201-2204
For a large impact parameter, the a-particle goes nearly undeviated and has a small deflection (q @ 0) The fact that only a small fraction of the number of incident particles rebound back indicates that the number of a-particles undergoing head on collision is small This, in turn, implies that the mass and positive charge of the atom is concentrated in a small volume Rutherford scattering therefore, is a powerful way to determine an upper limit to the size of the nucleus
9
2202-2205
The fact that only a small fraction of the number of incident particles rebound back indicates that the number of a-particles undergoing head on collision is small This, in turn, implies that the mass and positive charge of the atom is concentrated in a small volume Rutherford scattering therefore, is a powerful way to determine an upper limit to the size of the nucleus FIGURE 12
9
2203-2206
This, in turn, implies that the mass and positive charge of the atom is concentrated in a small volume Rutherford scattering therefore, is a powerful way to determine an upper limit to the size of the nucleus FIGURE 12 4 Trajectory of a-particles in the coulomb field of a target nucleus
9
2204-2207
Rutherford scattering therefore, is a powerful way to determine an upper limit to the size of the nucleus FIGURE 12 4 Trajectory of a-particles in the coulomb field of a target nucleus The impact parameter, b and scattering angle q are also depicted
9
2205-2208
FIGURE 12 4 Trajectory of a-particles in the coulomb field of a target nucleus The impact parameter, b and scattering angle q are also depicted Example 12
9
2206-2209
4 Trajectory of a-particles in the coulomb field of a target nucleus The impact parameter, b and scattering angle q are also depicted Example 12 1 In the Rutherford’s nuclear model of the atom, the nucleus (radius about 10–15 m) is analogous to the sun about which the electron move in orbit (radius » 10–10 m) like the earth orbits around the sun
9
2207-2210
The impact parameter, b and scattering angle q are also depicted Example 12 1 In the Rutherford’s nuclear model of the atom, the nucleus (radius about 10–15 m) is analogous to the sun about which the electron move in orbit (radius » 10–10 m) like the earth orbits around the sun If the dimensions of the solar system had the same proportions as those of the atom, would the earth be closer to or farther away from the sun than actually it is
9
2208-2211
Example 12 1 In the Rutherford’s nuclear model of the atom, the nucleus (radius about 10–15 m) is analogous to the sun about which the electron move in orbit (radius » 10–10 m) like the earth orbits around the sun If the dimensions of the solar system had the same proportions as those of the atom, would the earth be closer to or farther away from the sun than actually it is The radius of earth’s orbit is about 1
9
2209-2212
1 In the Rutherford’s nuclear model of the atom, the nucleus (radius about 10–15 m) is analogous to the sun about which the electron move in orbit (radius » 10–10 m) like the earth orbits around the sun If the dimensions of the solar system had the same proportions as those of the atom, would the earth be closer to or farther away from the sun than actually it is The radius of earth’s orbit is about 1 5 ´ 1011 m
9
2210-2213
If the dimensions of the solar system had the same proportions as those of the atom, would the earth be closer to or farther away from the sun than actually it is The radius of earth’s orbit is about 1 5 ´ 1011 m The radius of sun is taken as 7 ´ 108 m
9
2211-2214
The radius of earth’s orbit is about 1 5 ´ 1011 m The radius of sun is taken as 7 ´ 108 m Solution The ratio of the radius of electron’s orbit to the radius of nucleus is (10–10 m)/(10–15 m) = 105, that is, the radius of the electron’s orbit is 105 times larger than the radius of nucleus
9
2212-2215
5 ´ 1011 m The radius of sun is taken as 7 ´ 108 m Solution The ratio of the radius of electron’s orbit to the radius of nucleus is (10–10 m)/(10–15 m) = 105, that is, the radius of the electron’s orbit is 105 times larger than the radius of nucleus If the radius of the earth’s orbit around the sun were 105 times larger than the radius of the sun, the radius of the earth’s orbit would be 105 ´ 7 ´ 108 m = 7 ´ 1013 m
9
2213-2216
The radius of sun is taken as 7 ´ 108 m Solution The ratio of the radius of electron’s orbit to the radius of nucleus is (10–10 m)/(10–15 m) = 105, that is, the radius of the electron’s orbit is 105 times larger than the radius of nucleus If the radius of the earth’s orbit around the sun were 105 times larger than the radius of the sun, the radius of the earth’s orbit would be 105 ´ 7 ´ 108 m = 7 ´ 1013 m This is more than 100 times greater than the actual orbital radius of earth
9
2214-2217
Solution The ratio of the radius of electron’s orbit to the radius of nucleus is (10–10 m)/(10–15 m) = 105, that is, the radius of the electron’s orbit is 105 times larger than the radius of nucleus If the radius of the earth’s orbit around the sun were 105 times larger than the radius of the sun, the radius of the earth’s orbit would be 105 ´ 7 ´ 108 m = 7 ´ 1013 m This is more than 100 times greater than the actual orbital radius of earth Thus, the earth would be much farther away from the sun
9
2215-2218
If the radius of the earth’s orbit around the sun were 105 times larger than the radius of the sun, the radius of the earth’s orbit would be 105 ´ 7 ´ 108 m = 7 ´ 1013 m This is more than 100 times greater than the actual orbital radius of earth Thus, the earth would be much farther away from the sun It implies that an atom contains a much greater fraction of empty space than our solar system does
9
2216-2219
This is more than 100 times greater than the actual orbital radius of earth Thus, the earth would be much farther away from the sun It implies that an atom contains a much greater fraction of empty space than our solar system does Rationalised 2023-24 295 Atoms EXAMPLE 12
9
2217-2220
Thus, the earth would be much farther away from the sun It implies that an atom contains a much greater fraction of empty space than our solar system does Rationalised 2023-24 295 Atoms EXAMPLE 12 2 Example 12
9
2218-2221
It implies that an atom contains a much greater fraction of empty space than our solar system does Rationalised 2023-24 295 Atoms EXAMPLE 12 2 Example 12 2 In a Geiger-Marsden experiment, what is the distance of closest approach to the nucleus of a 7
9
2219-2222
Rationalised 2023-24 295 Atoms EXAMPLE 12 2 Example 12 2 In a Geiger-Marsden experiment, what is the distance of closest approach to the nucleus of a 7 7 MeV a-particle before it comes momentarily to rest and reverses its direction
9
2220-2223
2 Example 12 2 In a Geiger-Marsden experiment, what is the distance of closest approach to the nucleus of a 7 7 MeV a-particle before it comes momentarily to rest and reverses its direction Solution The key idea here is that throughout the scattering process, the total mechanical energy of the system consisting of an a-particle and a gold nucleus is conserved
9
2221-2224
2 In a Geiger-Marsden experiment, what is the distance of closest approach to the nucleus of a 7 7 MeV a-particle before it comes momentarily to rest and reverses its direction Solution The key idea here is that throughout the scattering process, the total mechanical energy of the system consisting of an a-particle and a gold nucleus is conserved The system’s initial mechanical energy is Ei, before the particle and nucleus interact, and it is equal to its mechanical energy Ef when the a-particle momentarily stops
9
2222-2225
7 MeV a-particle before it comes momentarily to rest and reverses its direction Solution The key idea here is that throughout the scattering process, the total mechanical energy of the system consisting of an a-particle and a gold nucleus is conserved The system’s initial mechanical energy is Ei, before the particle and nucleus interact, and it is equal to its mechanical energy Ef when the a-particle momentarily stops The initial energy Ei is just the kinetic energy K of the incoming a- particle
9
2223-2226
Solution The key idea here is that throughout the scattering process, the total mechanical energy of the system consisting of an a-particle and a gold nucleus is conserved The system’s initial mechanical energy is Ei, before the particle and nucleus interact, and it is equal to its mechanical energy Ef when the a-particle momentarily stops The initial energy Ei is just the kinetic energy K of the incoming a- particle The final energy Ef is just the electric potential energy U of the system
9
2224-2227
The system’s initial mechanical energy is Ei, before the particle and nucleus interact, and it is equal to its mechanical energy Ef when the a-particle momentarily stops The initial energy Ei is just the kinetic energy K of the incoming a- particle The final energy Ef is just the electric potential energy U of the system The potential energy U can be calculated from Eq
9
2225-2228
The initial energy Ei is just the kinetic energy K of the incoming a- particle The final energy Ef is just the electric potential energy U of the system The potential energy U can be calculated from Eq (12
9
2226-2229
The final energy Ef is just the electric potential energy U of the system The potential energy U can be calculated from Eq (12 1)
9
2227-2230
The potential energy U can be calculated from Eq (12 1) Let d be the centre-to-centre distance between the a-particle and the gold nucleus when the a-particle is at its stopping point
9
2228-2231
(12 1) Let d be the centre-to-centre distance between the a-particle and the gold nucleus when the a-particle is at its stopping point Then we can write the conservation of energy Ei = Ef as 2 0 0 1 (2 )( ) 2 4 4 e Ze Ze K d d ε ε = = π π Thus the distance of closest approach d is given by 2 0 2 4 Ze d εK = π The maximum kinetic energy found in a-particles of natural origin is 7
9
2229-2232
1) Let d be the centre-to-centre distance between the a-particle and the gold nucleus when the a-particle is at its stopping point Then we can write the conservation of energy Ei = Ef as 2 0 0 1 (2 )( ) 2 4 4 e Ze Ze K d d ε ε = = π π Thus the distance of closest approach d is given by 2 0 2 4 Ze d εK = π The maximum kinetic energy found in a-particles of natural origin is 7 7 MeV or 1
9
2230-2233
Let d be the centre-to-centre distance between the a-particle and the gold nucleus when the a-particle is at its stopping point Then we can write the conservation of energy Ei = Ef as 2 0 0 1 (2 )( ) 2 4 4 e Ze Ze K d d ε ε = = π π Thus the distance of closest approach d is given by 2 0 2 4 Ze d εK = π The maximum kinetic energy found in a-particles of natural origin is 7 7 MeV or 1 2 × 10–12 J
9
2231-2234
Then we can write the conservation of energy Ei = Ef as 2 0 0 1 (2 )( ) 2 4 4 e Ze Ze K d d ε ε = = π π Thus the distance of closest approach d is given by 2 0 2 4 Ze d εK = π The maximum kinetic energy found in a-particles of natural origin is 7 7 MeV or 1 2 × 10–12 J Since 1/4pe0 = 9
9
2232-2235
7 MeV or 1 2 × 10–12 J Since 1/4pe0 = 9 0 × 109 N m2/C2
9
2233-2236
2 × 10–12 J Since 1/4pe0 = 9 0 × 109 N m2/C2 Therefore with e = 1
9
2234-2237
Since 1/4pe0 = 9 0 × 109 N m2/C2 Therefore with e = 1 6 × 10–19 C, we have, 9 2 2 –19 2 12 (2)(9
9
2235-2238
0 × 109 N m2/C2 Therefore with e = 1 6 × 10–19 C, we have, 9 2 2 –19 2 12 (2)(9 0 10 Nm / )(1
9
2236-2239
Therefore with e = 1 6 × 10–19 C, we have, 9 2 2 –19 2 12 (2)(9 0 10 Nm / )(1 6 10 ) Z 1
9
2237-2240
6 × 10–19 C, we have, 9 2 2 –19 2 12 (2)(9 0 10 Nm / )(1 6 10 ) Z 1 2 10 J C C d − × × = × = 3
9
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0 10 Nm / )(1 6 10 ) Z 1 2 10 J C C d − × × = × = 3 84 × 10–16 Z m The atomic number of foil material gold is Z = 79, so that d (Au) = 3