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Read the following passage and answer the accompanying questions - Leaving Cert Physics - Question 11 - 2019

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Read the following passage and answer the accompanying questions. Physics Rivalries We tend to think of scientists as toiling away in their laboratories, not lookin... show full transcript

Worked Solution & Example Answer:Read the following passage and answer the accompanying questions - Leaving Cert Physics - Question 11 - 2019

Step 1

Explain why the transmission of electricity using low voltage is not economical.

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Answer

Using low voltage to transmit electricity results in high current flow. High current can lead to significant energy loss in the form of heat due to resistance in the conductors. The loss of energy can be calculated using the formula:

P=I2RP = I^2 R

where PP is the power loss, II is the current, and RR is the resistance. Therefore, to minimize energy losses during transmission, a higher voltage is needed, which results in lower current.

Step 2

Name the device used to (i) reduce a.c. voltage, (ii) convert current from a.c. to d.c.

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Answer

(i) Transformer (ii) Rectifier/Diode

Step 3

State Hooke's Law.

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Answer

Hooke's Law states that the restoring force is proportional to the displacement from equilibrium:

F=kxF = -kx

where FF is the restoring force, kk is the spring constant, and xx is the displacement.

Step 4

A ball of mass 110 g is travelling at a speed of 4 m s⁻¹. It rebounds from a wall and travels in the opposite direction at the same speed. The ball was in contact with the wall for 0.2 seconds. Use Newton's laws of motion to calculate the force exerted by the wall on the ball.

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Answer

First, calculate the change in momentum:

extChangeinmomentum=m(vfvi) ext{Change in momentum} = m(v_f - v_i)

where:

  • m=0.110m = 0.110 kg (mass in kg),
  • vf=4v_f = -4 m s⁻¹ (final velocity, negative as it's in the opposite direction),
  • vi=4v_i = 4 m s⁻¹ (initial velocity).

Calculating gives:

extChangeinmomentum=0.110kgimes(44)=0.110kgimes8=0.88kgextms1 ext{Change in momentum} = 0.110 kg imes (-4 - 4) = 0.110 kg imes -8 = -0.88 kg ext{ m s}^{-1}

Now, using the impulse-momentum theorem:

Fimest=extChangeinmomentumF imes t = ext{Change in momentum}

where t=0.2st = 0.2 s.

Solving for FF gives:

F = rac{ ext{Change in momentum}}{t} = rac{-0.88 kg ext{ m s}^{-1}}{0.2 s} = -4.4 N

Thus, the force exerted by the wall is 4.4 N in the opposite direction.

Step 5

A magnifying glass is a basic microscope. Draw a ray diagram to show the formation of an upright image in a magnifying glass.

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Answer

In the ray diagram, depict the lens and the object being magnified. Draw the following:

  1. Object placed within the focal length of the lens.
  2. Two rays emanating from the top of the object: one passing through the optical center of the lens, and the other refracted downward towards the focal point.
  3. The point where the extended rays appear to diverge from creates the image.

Indicate the 'upright' nature of the formed image on the diagram.

Step 6

A plutonium–239 nucleus undergoes nuclear fission when a neutron collides with it. Xenon–134 and zirconium–103 are produced together with some neutrons. Write a nuclear equation for this fission reaction.

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Answer

The nuclear equation for the fission reaction is:

ightarrow ^{134}_{54}Xe + ^{103}_{40}Zr + 3n$$

Step 7

Calculate the energy released in this reaction.

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Answer

Using the mass defect, we can calculate the energy released as follows:

  • Loss in mass = 3.3682 x 102810^{-28} kg
  • Using Einstein's equation:

E=mc2E = mc^2

First, calculate:

E=3.3682imes1028kgimes(2.9979imes108m/s)2E = 3.3682 imes 10^{-28} kg imes (2.9979 imes 10^8 m/s)^2

This results in: E=3.0271imes1011JE = 3.0271 imes 10^{-11} J

Step 8

In what form is this energy released?

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Answer

The energy is released in the form of kinetic energy during the fission process.

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