### Physics Past Questions

4826

ai. Define the electric potential at a point in an electric field.

ii.  An uncharged body, A, was charged electrostatically by a test charge, B, using the method of induction and the method of contact. State two differences between the two methods.

b. An important precaution during an electricity experiment is to open the circuit when no readings are being taken. Give two reasons for the stated precaution.

ci. Fig. 11.0 is a circuit diagram in which a coil of inductance, L, and a resistor of resistance, R, are connected to a variable alternating source of frequency, f.

The table shows the square of the impedance, $$Z^2$$; corresponding to each value of $$ƒ^2$$.

 $$ƒ^2$$/ $$Hz^2$$ 198.8 400 600.3 800.9 900 $$Z^2$$/ $$Ω^2$$ 249.6 400 550.3 702.3 800.9

Write down the equation for Z in terms of $$f^2$$, $$R^2$$, and $$L^2$$.

ii. Plot a graph $$Z^2 against \(f^2$$ of and use it to determine the values of:
i. L
ii. R
[$$π^2$$ = 10]

WAEC 2023
4827

a. State the function of each of the following parts of a modern x-ray tube: i. heater; ii. high tension source; iii. cooling fins.

b. State one reason for each of the following design features of a modern x-ray tube: i. the glass envelope is highly evacuated;  ii. the target is a metal of very high melting point; iii. the cooling fins are located outside the glass envelope.

c. In a nuclear fission reaction, a nuclide $$^{235}U_{92}$$ is bombarded with a neutron to produce $$^{93}Kr_{36}$$ and $$^{141}Ba_{56}$$ with additional neutrons, the energy involved in the process is Q.
[mass of $$^{235}U_{92}$$ = 235.044 u, mass of $$^{93}Kr_ {36}$$ = 91.898 u, mass of $$^{141}Ba_ {56}$$ = 140.914 u,
mass of neutron = 1.009u, 1u = $$1.66 \times 10^{27}$$ kg, c = 3.0 × $$10^8ms^1$$]
i. Write down the balanced nuclear reaction equation for the process.

ii. State with reason whether Q is absorbed or released in the process.

iii. Calculate the value of Q in joules.

WAEC 2023
4828

A metal sphere is placed on an insulating stand. A negatively charged rod is brought close to it. If the sphere is earthed and the rod is taken away, what will be the charge on the sphere?

• A. The sphere will remain neutral.
• B. The sphere will have a net negative charge.
• C. The sphere will have a net positive charge.
• D. The sphere will become polarized
JAMB 2023