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kogti [31]
3 years ago
6

Imagine an alternative universe where the characteristic decay time of neutrons is 3 min instead of 15 min. All other properties

remain unchanged from what was discussed in class.
(a) Show that the maximum possible value of the primordial helium fraction is: Ymax = 2f 1 + f (1) where f = nn/np ≥ 1 is the neutron-to-proton ratio at the time of nucleosynthesis. Prove that this assertion is true.
(b) Estimate the maximum fraction of the baryonic matter in the form of helium today. You may assume all He nuclei exist in the form of helium 4
Physics
1 answer:
FrozenT [24]3 years ago
6 0

Answer:

(a) [Y_{p} ]_{max} = \frac{2f}{1+f}

(b) f_{new} = 0.013; [Y_{p} ]_{max} = 0.026

Explanation:

Since the neutron-to-proton ratio at the time of nucleosynthesis is given:

f = \frac{n_{n} }{n_{p} }

Therefore:

n_{n} = f*n_{p}

Then, to determine the maximum ⁴He fraction if all the available n_{n} neutrons bind to all the protons. Since, there are 2 protons and 2 neutrons in a ⁴He nucleus, it shows that there would be n_{n}/2 nuclei of ⁴He.

In addition, a ⁴He nucleus has a mass of 4m_{p}, where m_{p} is the mass of one proton. Thus, n_{n}/2 nuclei of such nuclei will have a mass of n_{n}/2*4m_{p}.

Assuming that m_{p}=m_{n}, there would be a total of (n_{n}+n_{p}) protons and neutrons with a total mass of (n_{n}+n_{p})*m_{p}.

Thus:[Y_{p} ]_{max} = \frac{2f}{1+f}

(b) Given:

t_{nuc} = 200 s;   τ_{n} = 3*60s = 180 s

f_{new} = \frac{n_{nf} }{n_{pf} } = \frac{exp (-200/180)}{5 +[1- exp(-200/180)]} =\frac{0.077}{5.923} = 0.013

[Y_{p} ]_{max} = \frac{2f}{1+f} = (2*0.013)/(1+0.013) = 0.026

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Very easy physics maths about current and other stuffs only one question please help me
Reil [10]

Answer:

The total voltage of the circuit is 18 volts.

Explanation:

We have, three identical resistors of resistance 3 ohms are connected in series in a circuit.

For a series combination, the equivalent resistance is given by the sum of individual resistances i.e.

R_{eq}=R_1+R_2+R_3\\\\R_{eq}=3+3+3\\\\R_{eq}=9\ \Omega

Let V is the voltage of the battery if the current in the circuit is 2 A. So,

V=IR

V=2\times 9\\\\V=18\ V

So, the total voltage of the circuit is 18 volts.

7 0
2 years ago
To identify whether the forces are balanced or not, you need to whet
jok3333 [9.3K]

Answer:

what are you asking?

Explanation:

7 0
2 years ago
Your teacher (175kg) and the lab (15kg) are 2m apart. What is the gravitational force between them? Draw a FBD, and label
Pachacha [2.7K]
The gravitational force between two objects is given by
F=G \frac{m_1 m_2 }{r^2}
where
G is the gravitational constant
m1 and m2 are the masses of the two objects
r is the separation between the two objects

In this problem, m_1 = 175 kg, m_2 =15 kg and r=2 m, therefore the gravitational force between the two objects is
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7 0
2 years ago
The core of a 400 Hz aircraft transformer has a net cross-sectional area of 13 cm2. The maximum flux density is 0.9 T, and there
jenyasd209 [6]

Answer:

32.76 Volt

Explanation:

frequency, f = 400 Hz

Area of crossection, A = 13 cm²

Maximum flux density, B = 0.9 tesla

Number of turns in secondary coil, N = 70

Let the maximum induced voltage is e.

According to the Faraday's law of electromagnetic induction, the induced emf is equal to the rate of change of magnetic flux.

e = dФ/dt

e=\frac{NBA}{t}

Time is defined as the reciprocal of frequency.

So, e = N B A f

e = 70 x 0.9 x 13 x 10^-4 x 400

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4 0
3 years ago
On Mars, where air resistance is negligible, an astronaut drops a rock from a cliff and notes that the rock falls about d meters
dimulka [17.4K]

Answer:

d_1 = 16 d

Explanation:

As we know that initial speed of the fall of the stone is ZERO

v_i = 0

also the acceleration due to gravity on Mars is g

so we have

d = v_i t + \frac{1}{2}gt^2

now we have

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now if the same is dropped for 4t seconds of time

then again we will use above equation

d_1 = 0 + \frac{1}{2}g(4t)^2

d_1 = 16(\frac{1}{2}gt^2)

d_1 = 16 d

7 0
3 years ago
Read 2 more answers
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