Correct Answer: C. 8.0 x 10² v

Explanation

V = \(\frac{W}{Q}\)

V = \(\frac{8 \times\ 10^{-2}}{100 \times\ 10^{-6}}\)

V = 8.0 x 10\(^2\) v

Correct Answer: A. is positively charged and is concentrated in a tiny volume

Explanation

In the experiment, when alpha particles were fired at a thin gold foil, most of the alpha particles passed straight through, but a few were deflected considerably. This result led Rutherford to conclude that the positive charge of the atom is concentrated in a small, dense nucleus at the center of the atom. The fact that some alpha particles were deflected strongly indicated that there was a positively charged nucleus within the atom. This experiment was crucial in developing our understanding of atomic structure and led to the model of the atom with a central nucleus containing protons and neutrons, surrounded by electrons.

Correct Answer: B. decrease

Correct Answer: A. mv2/r

Explanation

(a)

The step-down transformer has more turns in the primary turns than in the secondary turns. It works by electromagnetic induction, the magnetic flux from the primary coil in the iron core links the secondary coil. When an alternating e.m.f \(E_{p}\) is connected to the primary coil, an alternating current flows. This produces corresponding variation of magnetic flux in the iron core which links the secondary coil. An induced e.m.f \(E_{s}\) of the same frequency as \(E_{p}\) is obtained. From Faraday's law, the e.m.f induced in a coil proportional to the rate of change of the magnetic flux linking the coil. So,

\(\frac{E_{s}}{E_{p}} = \frac{N_{s}}{N_{p}}\). \(N_{s}\) - Number of turns in secondary coil; \(N_{p}\) - number of turns in primary coil.

(b) Three ways by which energy is lost and how they can be minimised are:

(1) Energy is lost through Eddy current produced in the soft — iron. This is reduced by laminating the core in thin strips. (2) Heat generation in the copper coils. This is reduced by using copper coils with low resistance. (3). Loss of energy due to reversal of iroes of force. This is reduced by using soft magnetic materials for the core.

(c)(i) Using \(\frac{E_{p}}{E_{s}} = \frac{N_{p}}{N_{s}}\)

\(\frac{4400}{220} = \frac{N_{p}}{N_{s}}\)

The ratio of the primary turns to the secondary turns is 20 : 1.

(ii) \(Efficiency = \frac{\text{power output}}{\text{power input}}\)

\(\frac{95}{100} = \frac{60}{input}\)

\(\text{Power input} = \frac{6000}{95} = 63.2W\)

\(\therefore Current I = \frac{P}{V} = \frac{63.2}{4400}\)

\(I = 0.0144A = 14.4 mA\)

Correct Answer: B. mass

Explanation

It is a type of beam balance with great precision, and it can pick up the slightest mass placed on it.

Explanation

(a) If a stable element is bombarded by \(\alpha\) - particles the nucleus will become unstable and decay into other elements with the release of energy.

Example; \(^{14}_{7}N + ^4_2He \to ^{17}_8 O + ^1_1H\) + Energy

(b) When the nucleus of Uranium is bombarded with a neutron, it splits into two nearly equal parts with a release of energy and neutrons. These excess neutron, if not controlled, further bombard the remaining nuclei, causing a chain reaction and consequently an explosion, provided the critical mass of the Uranium is, exceeded

\(^{235}_{92}U + ^1_0U \to ^{236}_{92}U \to ^{141}_{56}Ba + ^{92}_{36}Kr + 3^1_0n\) + Energy

(c)(i) Radioactive substances give off identifiable radiation i.e \(\alpha, \beta\) and 8 radiations

(ii) They are chemically identical to their non-radioactive counterparts and later can be made radioactive by bombardment with nuclear particles

(iii) Radioactive materials decay with specific half-life.

(d) Three applications of atomic energy

(i) It is used for the production of nuclear weapons for warfare

(ii) It is used in the generation of electric power

(iii) It is used to detect leakages in underground pipes carrying oil or gases.

(e) Two Postulates of Bohr's Model of the Atom:

(i) Electrons occupy certain fixed orbits around the nucleus of an atom. When an electron is in one of these orbits it does not radiate any energy

(ii) The angular momentum is quantized in the allowed orbit.

Two Limitations To Bohr's Model:

(i) It could not interpret the details of the spectra of complex atoms

(ii) There is no theoretical basis for selecting the allowed orbits postulated.

Correct Answer: B. brass

Correct Answer: D. 30.75cm³

Explanation

\(V_2 = \frac{P_1V_1T_2}{P_2T_1} = \frac{9.52 \times 10^4 \times 40 \times 273}{1.034 \times 10^5 \times 327}\)

= 30.75cm³

Correct Answer: C. 148.50m

Explanation

v = 2x/t ? distance x = vt/2 = 148.5m