# 2018 - WAEC Physics Past Questions and Answers - page 5

The circuit contains three ammeters A1, A2 and A3 with readings of A2 and A3 shown as indicated in the diagram. Determine the reading of A1.

2A

3A

5A

8A

**correct option:**b

For Ammeters that are connected in series:

A3= A2 + A1

A1 = A3 - A1

= 5A - 2A

= 3A

Which of the following statements about magnetic lines of force is not correct? They

In which of the following activities is an induction coil not useful?

**correct option:**d

In a series R-L-C circuit, R = 10\(\Omega\), \(X_{c}\)= 4\(\Omega\) and \(X_{L}\) = 9\(\Omega\). The impedance of the circuit is

4.1\(\Omega\)

5.0\(\Omega\)

10.8\(\Omega\)

11.2\(\Omega\)

**correct option:**d

The impedance (Z) for a RLC circuit is:

\(Z = \sqrt{R^{2} + (X_{L} - X_{C})^{2}}\)

= \(\sqrt{10^{2} + (9 - 4)^{2}}\)

= \(\sqrt{125}\)

= 11.18\(\Omega\) \(\approxeq\) 11.2\(\Omega\)

A student uses two compass needles to investigate the magnetic field around a bar magnet. Which of the following diagrams show the correct directions of the needles?

A

B

C

D

**correct option:**b

The field direction is taken to be outward from the North pole and in to the South pole of the magnet and, they form closed lines.

Which of the following is emitted in a process of natural radioactivity?

\(\alpha\)- particles and \(\beta\)- particles

\(\alpha\)- particles and X-rays

\(\beta\)- particles and X-rays

\(\lambda\)- rays and X-rays

**correct option:**a

In natural radioactivity, alpha, beta and gamma rays are emitted.

In which of the following situations is photoelectric effect employed?

I. Automatic devices for switching on light at dusk

II. Automatic doors in departmental stores

III. Automatic devices for switching on air conditioners

IV. Automatic voltage stabilizers

**correct option:**a

Which of the following radiations has the longest wavelength?

**correct option:**b

Radio wave has the longest wavelength and shortest frequency.

In which of the following fields is radioisotopes not used?

**correct option:**d

A nuclide is represented by \(_{32}^{70}B\). Determine its neutron-proton ratio

0.5

0.8

1.2

1.5

**correct option:**c

The element B has a mass number 70 and atomic number 32.

Hence, B has 32 protons and (70-32) = 38 neutrons.

The neutron to proton ratio is 38:32 = \(\frac{38}{32} = 1.1875\)

\(\approxeq 1.2\)