Search Results (9 total)

Preinstruction SAT scores and normalized gains (G) on the force concept inventory (FCI) were examined for individual students in interactive engagement (IE) courses in introductory mechanics at one high school (N=335) and one university (N=292), and strong, positive correlations were found for both populations (r=0.57 and r=0.46, respectively). These correlations are likely due to the importance of cognitive skills and abstract reasoning in learning physics. The larger correlation coefficient for the high school population may be a result of the much shorter time interval between taking the SAT and studying mechanics, because the SAT may provide a more current measure of abilities when high school students begin the study of mechanics than it does for college students, who begin mechanics years after the test is taken. In prior research a strong correlation between FCI G and scores on Lawson’s Classroom Test of Scientific Reasoning for students from the same two schools was observed. Our results suggest that, when interpreting class average normalized FCI gains and comparing different classes, it is important to take into account the variation of students’ cognitive skills, as measured either by the SAT or by Lawson’s test. While Lawson’s test is not commonly given to students in most introductory mechanics courses, SAT scores provide a readily available alternative means of taking account of students’ reasoning abilities. Knowing the students’ cognitive level before instruction also allows one to alter instruction or to use an intervention designed to improve students’ cognitive level.

Quartz-crystal microbalance isotherms of ⁴He on rubidium are presented. The isotherms are used to locate the prewetting transition and the onset of superfluidity in the adsorbed helium films. The phase diagram of He on Rb is distinctly different from helium on either conventional strong substrates or on cesium. In particular, the superfluid transition is hysteretic and does not conform to the Kosterlitz-Thouless paradigm.

Conditions of global energy and pressure balance are applied to a cylindrically symmetric plasma column having a B_θ confining field and a B_z stabilizing field, as exist in stabilized z pinches and tokamaks. In the process of producing stable configurations the plasma pressure due to Ohmic heating during magnetic field diffusion may become too large for the confining field to contain.

Experimental values for the ratios of the positive, natural, and negative components have been obtained for proton beams in the energy region 3-200 kev emerging from Al, Be, Ca, Ag, Au, and SiO foils. Clean surfaces were obtained by evaporating fresh material onto the foil during a run. As expected, the equilibrium charge ratio appears to be determined by the last few (∼5) atoms on the exit side of the foil. At 37±3 kev, the positive and neutral components are equal for all materials tested, except Ca (18±2 kev). Significant differences have been found in the charged components from these metals. The observed ratios of the components for different metals parallel their work functions at proton energies >100 kev.

These cross sections were measured by the process of passing a deuteron beam into a thin gas target contained behind a thin window of evaporated silicon monoxide. The energy loss in the window was measured by a deceleration technique. Charged particles from the reactions were observed at 90° in the laboratory system with proportional counters. Some results are as follows: for the reaction D(d, p)T, by use of the angular distribution reported by Wenzel and Whaling, the total cross section σ is 15.4 mb with a probable error of 3.2 percent at 100-kev incident deuteron energy; σ=0.629 mb±5 percent at 25 kev. For the reaction D(d, n)He³, σ=15.2 mb±3.2 percent at 100 kev; σ=0.592 mb±5 percent at 25 kev. The sum of these two cross sections follows a Gamow function below 50 kev. For the reaction T(d, n)He⁴, isotropy in the center-of-mass system being assumed, σ shows a peak value of 4.95 barns±2.8 percent at 107 kev; at 40 kev, σ=0.72 barn±3.2 percent; at 19 kev, σ=0.045 barn±5 percent; below 19 kev, σ follows a Gamow function. For the reaction He³(d, p)He⁴ with isotropy assumed, σ=16 mb±3 percent at 93 kev; σ=0.124 mb±5 percent at 36 kev; and σ follows a Gamow relation below 100 kev.

Experimental values for the energy loss of protons in H₂, He, N₂, O₂, A, Kr, H₂O, CO₂, and CCl₄ have been obtained in the region from 10 to 80 kev. The energy loss (ΔE / Δx) can be expressed for the elementary gases measured in terms of a single curve, with two constants ΔE / Δx=Lf(ME). The energy loss per atom is independent of the target density over the range 0 to 1.5-mm Hg, and the energy loss for compound gases is equal to the sum of their components.

A study of the photo-disintegration of the deuteron using a cloud chamber as a detector has been made for gamma-ray energies of 6.14 and 7.00 Mev from the F(p,α)O^16* reaction. By observing the number of photo-disintegration protons and the number of electron pairs formed in the gas (CD₄) of the cloud chamber, the ratio of the photo-disintegration cross section to the pair cross section is obtained. Assuming a calculated value for the pair cross section these data yield σ[D(γ,p)n]=25.7(14 percent P . E.)×10^-28 cm² at an average gamma-ray energy of 6.55 Mev.

A plot of the angular distribution of the photo-disintegration protons agrees, within statistical limits, with sin²θ, though there may be a slight asymmetry in the forward direction.

The ratio, R=σ-pairs / σ-triplets=C(Z²)_ef / Z_ef for three gases, CH₄, air, and argon, has been studied and C found to be 3.63, 3.97, and 4.11, respectively. The average value of C from these data is 3.92±0.26. The gamma-rays from F¹⁹(p,α)γO¹⁶ were used in this experiment. The measured energies of the gamma-rays as deduced from pairs formed in CH₄ are 6.13±0.06 and 7.12±0.07 Mev. Data on the energy distribution of the low energy negative electron of the triplet are included.